I've seen Reigate Heath and I really must play it, for it looks superb.
Some they missed that I'd happily play anytime. (Can't say that of all the courses on the normal top 100 GB&I)
West of London
Thames Ditton and Esher - true unwatered heath.
http://www.thamesdittonandeshergolfclub.com/Locations_View.aspx?Locationid=3Moore Place (brother speaks highly of it)
East London
Crowlands Heath (good despite the name)
Hobbs X
East Anglia
Sutton Bridge - plays into and out of an enormous Victorian dry dock.
Wales
CWMRHYDNEUADD GOLF CLUB - my tip for the hidden gem. Plays down and back up a long valley, with crossing holes. Lovely.
Hard to rate these as lengths and suitibilty for 2 varied rounds varies so much. However it's nice to see them given their due.
PS Does the Balgrove merit it's inclusion? I can think of 100 things I'd rather do in St Andrews before I even considered it.