Walthamstow is pretty pricey, and is much bigger than I thought - it's got like about 5 stations.
I spent ages looking for a place to buy - started in Walthamstow and moved further and further towards the river until we got a place in East Ham. The area is OK - kind of like Sparkhill was about 10 years ago. It was more or less the only place we could afford, given the craziness of people offering 20% over asking price. I saw a 2 bed flat in Walthamstow on for £285k, eventually get sold for £385k. I wouldn't suggest renting / sharing in East Ham though - more just a way of getting on the ladder.
If you are looking for a short term share, you should have a look at Statford. There are loads of flats that people have snapped up in the Olympic Village, which have spare rooms, as they look to soften the blow of the mortgage.
The transport links are pretty good - Canary Wharf, The City, Dalston, H&I and Oxford Circus are all on direct trains / tubes. The social scene is getting better there as well. Granted, there are still a few shit holes, although nowhere near as many as where I am now.