If you don't mind being a bit further out: Epsom. You won't feel like you're 'in London' (Good or bad depending on how you view it), but you have a choice of two train lines to either Waterloo or Victoria in 35 mins, good rail connections to almost anywhere in the South East and are only a couple of stops from Dorking in the other direction for Surrey Hills biking goodness.
You'll also get a lot more for your money.
£1000pcm in Clapham will get you sod all. I was paying £1200 for a 1 Bed back in 2004.