I've been looking for a way to track my bankroll for a few years. Before, I tried to keep track of it through Microsoft Excel. But it proved to be too tedious. Recently, I've found an easier way. This is through an iPod application called Poker Income.
Poker Income can show hourly rate, which games are worth playing, it tells you how you're running, etc. Everything I was looking for in a bankroll tracker. And it's right in my pocket. No need to remember my playing details until I get home to my laptop.
I'd definitely recommend getting this app even if you're just a casual poker player. Get this at the App Store.