Unlike other people in this thread I'm not going to spam the site connected to the company that I work for. Any of the sites that come up in the top 5 have great reputations and you can't go wrong with any of them. I can't say the others are bad, I have not heard of most of them and I bet many of them are skins of the top sites.
http://www.google.com/search?hl=en&q...poker+bankroll
Disclaimer: One of those sites is connected to the company I work for. I do not work for that division or profit anything from it but I still feel it is better to show all of the choices.