I have to agree that Pokerstars is the best for a low limit player. Nowhere else online can you invest 1 dollar and have the potential to win as much. Every day there are dozens of tournaments with 1 dollar or less buy-ins with thousands of people entering. You can play tournaments or you can play in ring games for as little as .01/.02 cents per hand.
Pokerstars also has LOTS of freeroll tournaments every day in all types of games, so you can play without even making any deposit at all. It is conceivable, although difficult, that you could win money on Pokerstars without making a deposit at all by making it far enough in the freerolls. Good luck and see you at the tables!!