Quickmin is an app that will keep track of your min and warn you if you are getting low. This is best used with a family plan I would think unless you are on your cell phone ALL the time. 

What I really like about this app though is it uses a badge on the application icon to let you know how many minuets you have left.  Sweet!  I would not use this myself because I have TONS of rollover minutes and thus do not pay attention. The only thing that kinda bothers me about this app is that I have to give my AT&T password.  I have been getting more and more nervous about giving out my information on anything and unless its something that I would really need, like having a family plan and a bunch of teenagers, I would give this a miss and just look things up on the interwebs.

But what I would REALLY like to see is an app like this that keeps track of how data you have downloaded and use a badging system like Quickmin.  Now since I have the AT&T unlimited plan, I really do not need to worry about it.  And in fact,  there is an app that keeps track of how much you have downloaded without having to go to settings to look it up called Meter.  I have not tried it yet, but I may give it a go and see how well it works and then report back here later.