CeX (Cex.co.uk) is on Rathbone Place
Game Focus (gamefocus.coo.uk) is on Goodge Street
As for social places, I can find any kind of bar I want on one small fairly unknown strip of road called Inverness Street in Camden. Come out of Camden Town station (right exit), turn right again and left where Virgin Megastore and Offspring are. This road has a spanish tapas bar that serves Sangria and has Falmenco drummers on Monday, A Brazillian bar with a pet parrot, a non-smoking Polish bar, a hip hop and breaks grafitti bar, a Malaysian restaurant with weird cocktails and nice food, a chilled European 'nu bar' with stunning waitresses and a mellow crowd and a trashy rock pub on the corner.
Otherwise, check out Cottons in Chalk Farm road for 150 different kinds of rum and AMAZING curried goat and other such awesome Carribean delicacies.