Peerages with "of" in the title
I believe the list I give below to include every title in general use in which it is correct to add the territorial designation. There are others, probably a fair number, submerged among the minor titles of other peers, but as they are never used, even as courtesy titles, there is no point in including them:
Curzon of Kedleston (a Viscountcy and a Barony of Curzon were already held by Earl Howe. The Marquessate is now extinct, but the title is still held by the late peer's widow).
Baldwin of Bewdley (by special permission to the former Prime Minister).
Lloyd-George of Dwyfor (by special permission to the former Prime Minister).
Mountbatten of Burma (by special permission).
Temple of Stowe (an earldom of Temple had previously been held in the same family, that of the Dukes of Buckingham and Chandos, a title now extinct).
Alexander of Hillsborough (there was already in existence the Viscountcy of Alexander of Tunis, q.v.).
Alexander of Tunis (there was a Scottish Barony of Alexander associated with the Stirling Earldom and Viscountcy, all dormant since the early eighteenth century. Moreover, Viscount Alexander is a customary style used for the heir to the Earl of Caledon, head of this Lord Alexander's family).
Bertie of Thame (the style of Lord Bertie had previously been in use as the courtesy title of the heir to the Earldom of Lindsey in the same family).
Bruce of Melbourne (there is a Bruce Earldom as well as several Bruce baronies in existence).
Cecil of Chelwood (there is a Cecil Barony in the same family attached to the Salisbury Marquessate).
Colville of Culross (so styled in the original patent of 1640. The first Baron - the Viscountcy came in 1902 - obtained a grant of the lands of Culross).
Cunningham of Hyndhope (there is a Marquess Conyngham, who is also Lord, Viscount and Earl Conyngham, pronounced in the same way, and there was a Scottish Barony of Cunningham of Kilmaurs associated with the long dormant Earldom of Glencairn).
FitzAlan of Derwent (there is a Barony of FitzAlan in the same family attached to the Norfolk Dukedom).
Horne of Slammanan (a Barony of Horne had previously been held by one of the famous commanders in the 1914-18 war; it became extinct on his death eight years before this Viscountcy was created for Sir Robert Horne).
Lee of Fareham (to avoid confusion with the Barony of Leigh).
Montgomery of Alamein (the Earl of Pembroke is also Earl of Montgomery; and the Earl of Eglinton and Winton is also Lord Montgomerie - a style for the heir).
Portal of Hungerford (there was another Lord Portal, with whom this family is not connected).
Runciman of Doxford (his father had previously been created Lord Runciman).
Wilmot of Selmeston (an Irish Viscountcy and an English Barony of Wilmot were held by Henry Wilmot, later Earl of Rochester, who fought for Charles I and was father of the famous wit and rake who was a favourite of Charles II. These titles became extinct in 1681).
Younger of Leckie (by special permission).
Allen of Hurtwood (there had been previously both a Barony and a Viscountcy of Allen, now extinct, in the peerage of Ireland).
Amherst of Hackney (taken from family surname, but there was already an Earldom of Amherst of existence).
Ashton of Hyde (there was already a Barony of Ashton in existence; it is now extinct).
Asquith of Bishopstone (life peerage conferred on Sir Cyril Asquith on his appointment as a Lord of Appeal in Ordinary. There is a Viscountcy of Asquith attached to the Earldom of Oxford in the same family).
Balfour of Burleigh (created in that style in 1607. Owned the lands of Balfour).
Balfour of Inchyre (there were already a Balfour Earldom and Barony).
Banbury of Southam (taken from the surname, but there had been an Earldom of Banbury which is possibly dormant but probably extinct).
Brabazon of Tara (a Barony of Brabazon, of Ardee, is held by the Earl of Meath).
Brassey of Apethorpe (there had been a previous Brassey Barony and a Brassey Earldom in the family, both extinct).
Brooke of Oakley (there are an Earldom and Barony of Brooke attached to the Warwick Earldom).
Clifford of Chudleigh (to distinguish the Barony from that of the Lords de Clifford and from previous Baronies of Clifford).
Cochrane of Cults (there were already two Cochrane Baronies in the family - that of the Earls of Dundonald).
Cullen of Ashbourne (there had previously been a Viscountcy of Cullen in the family).
Douglas of Barloch (see Douglas of Kirtleside)
Douglas of Kirtleside (there was a Dukedom of Douglas and there still are a Marquessate of Douglas and various Douglas Baronies).
Fairfax of Cameron (a note in Volume 5 of The Complete Peerage says: "It is so given - Lord Fairfax of Cameron - in the appendix to Wood's Douglas, though in the body of the work it is given as 'Baron Fairfax of Cameron'. Possibly the correct form is 'Lord Fairfax, Baron of Cameron'." That is plausible. When a year later, in 1628, another Fairfax was created a viscount and desired to retain his name in his title, he was styled Viscount Fairfax of Emley, which, under the rule to which I have referred, would seem to indicate that there was already, or had been, a peerage of Fairfax. If The Complete Peerage is right, the "of Cameron" would be inaccurate in the conventional style - see references to the Baronies of Brabazon and Graves earlier in this section - but, right or wrong, it is now clearly sanctioned by custom).
Fraser of North Cape (a previous Barony of Fraser existed in the seventeenth and eighteenth centuries)
Grey of Groby (courtesy style of eldest son of Earls of Stamford; there are two older Baronies of Grey)
Hamilton of Dalzell (previous Hamilton Baronies in existence)
Hardinge of Penshurst (there was already a Viscountcy of Hardinge in the family)
Howard of Glossop (previous Howard Baronies in existence)
Howard of Penrith (see Howard of Glossop)
Hunsdon of Hunsdon (there had been a previous Hunsdon Barony, though long extinct)
Lindsey of Birker (there was already an Earldom of Lindsey, held by the Earl of Abingdon. There is also a Scottish Earldom of Lindsay, with which is held a Barony of Lindsay).
Lucas of Chilworth (see Lucas of Crudwell)
Lucas of Crudwell (a title bestowed in the seventeenth century on Mary Lucas, daughter of a Lord Lucas whose barony became extinct with the death of his brother and heir).
Lyle of Westbourne (to distinguish it from the similar-sounding Baronies of Lisle and Lyell).
Macdonald of Gwaenysgor (there was and still is an Irish Barony of Macdonald, and towards the end of the last century there was a Barony of Macdonald of Earnscliffe created for the widow of the famous Sir John Macdonald, the first Prime Minister of the Dominion of Canada).
Mackintosh of Halifax (though there has not been a previous Mackintosh peerage, there is a Scottish Law Lord who bears the style of Lord Mackintosh, but consideration was also taken of the existence of the famous Scottish chieftain, Mackintosh of Mackintosh. By Scottish custom he is referred to merely as Mackintosh and so signs himself. Garter King of Arms therefore, in conjunction with Lyon King of Arms, advised that it would not be right to allow the then Sir Harold Mackintosh to become Lord Mackintosh plain and simple).
Macpherson of Drumochter (as in the case of Mackintosh of Halifax, regard was held to the existence of the Chief of the Clan Macpherson).
Mildmay of Flete (created in this style in 1932 by special permission).
Montagu of Beaulieu (in the past there have been Montagu titles in every rank of the peerage, from baron to duke, and there is still a Barony of Montagu of Kimbolton held by the Duke of Manchester, and a Barony of Montagu of St. Neots held by the Earl of Sandwich).
Monteagle of Brandon (there had been a previous Barony of Monteagle in the Stanley family, and the Marquess of Sligo holds two Baronies of Monteagle).
Morris of Kenwood (there was already a Morris Barony, created in 1918 for a former Prime Minister of Newfoundland).
Morton of Henryton (a life peerage held by a Lord of Appeal in Ordinary. A Scottish Earldom of Morton has existed since 1458).
Napier of Magdala (there was already a Scottish Barony of Napier).
Ponsonby of Shulebrede (taken from the surname, but there is another Ponsonby Barony in the family, that of the Earls of Bessborough).
Ritchie of Dundee (another special case. Created so in 1905).
Russell of Liverpool (there were already Russell baronies attached to the Bedford Dukedom, there was a Russell Earldom, and there had been a Russell life peerage).
Ruthven of Canberra (courtesy style of heir to Earldom of Gowrie; there were already two Ruthven baronies in the same family).
St. John of Bletso (there was already in existence a Barony of St. John of Basing attached to the Winchester Marquessate).
Saltoun of Abernethy (created in that style in 1445).
Simon of Wythenshawe (a Viscountcy of Simon was already in existence).
Stanley of Alderney (there were previously Stanley baronies in existence).
Strange of Knokin (about the same time - 1299 - there was a Barony of Strange of Blackmere, now extinct, but, as explained in another section, in 1628 another Barony of Strange of Knokyn (now attached to the Atholl Dukedom) was created in error).
Vaux of Harrowden (evidently a special case, for the barony was created in that style in 1523).
Warrington of Clyffe (there had been two Earldoms of Warrington, both now extinct, the last attached to the Earldom of Stamford).
This list was created by Heywood almost fifty years ago and matters have changed considerably since then. In particular the 1958 Life Peerages Act has been responsible for the creation of a large number of Life Peerages. A very large number of the Life Peers created since 1958 have used their surname as the title of their peerages. As a consequence many Life Peers have had to qualify their title with a territorial designation, e.g. Wilson of Rievaulx, Archer of Weston-super-Mare, etc.