Friendly little place at the end of Walton Street. (It's actually on Kingston Road, because it's just the other side of the mini-roundabout, but it's still logically Walton Street.) The first few times I've been in, I was overwhelmed by the range of beers, but now I've got used to it and probably sampled around two-thirds of it.
They've certainly got an excellent selection of English beers, with the whole Hook Norton range available and a few interesting things around as well. Some beers are available in polypins. My beer-of-choice, Asahi, is available for 99p a bottle, which isn't bad at all, and they also sell it in crates. Plenty of German and Belgian stuff available as well, and also more off-beat stuff. (Mexican, Dutch, African and occasionally Russian.)
A fantastic place to stop in on your way to the Bombay. In late September 2003, it was taken over by new management, but the stock remains the same and the range seems, if anything, to have improved. And they're now open until 11. Bonus.