I tried a few apps out and liked this one best. Some of the others I tried had more features, but I love how the default view is just totals of each category with whats left still to spend that month (or week or day, you can pick), which is all I need. I was able to set up separate "accounts" to use as an emergency fund and a travel fund, and can transfer whats left at the end of the month to those. It can be locked with a passcode, it has everything I need. If youre looking for an app that lets you set a monthly budget that has goals for each category, this isnt the app for you, but I prefer this set-up because I only care whether I stayed in budget at the end of the month.
Bonye101 about Money Tracker - A weekly budget planner