Recommended web sites that help pick out interior wall colors?
I'd second Greebo's suggestion of buying samples, but we've found that painting lining paper works better.

Firstly, you can move the patch around the room to see it in the different conditions that exist in your room - next to window, in the dark corner beside the chimney, etc.

Secondly, you don't have to worry about a darker colour showing through if you end up choosing a lighter colour.

Thirdly, you can reuse the sample in another room or even in someone else's house.