I seem to remember the last couple of Payday sales at Gameplay being pretty good - although you will probably need to get in early to snarf the best bargains, as per usual.
Probably worth a look tomorrow morning anyways (starts 9am Thursday)
EDIT: Some good prices there, imho (I sure others will disagree.....)
Madworld Wii £14.98
Far Cry 2 £14.98
Prince of Persia £14.98
Fifa 09 £14.98
360 Wireless controllers £17.98