I have created a d20 Ability Calculator for Android (http://www.heikkitoivonen.net/android/d20abicalc/). If you use a point buy system similar to the Dungeons & Dragons 3.5e DMG p. 169, you can configure the points for your campaign and use your Android-powered mobile device to come up with the optimal ability scores for your character with just a few taps of the screen. Easy to use, no network required, help files included (although I doubt you'll need them). Sells for $0.99 USD.
Not for D&D 4e!
If you have any ideas on how to improve the program, please let me know!