I've written this app for a few platforms - and am using it to jump into the Android Development world.
Here's the App Brain Link
Or just search the market for Pimorize
Still pre 1.0 version: I haven't added all the features I think it should have to be called 1.0 - but it works and it's currently helping me memorize Pi.
Note: I am aware that knowing more than 10 digits of Pi is pretty much a waste of time... and so is my high score in galaga: But I've been surprised how many times Pi comes into a normal conversation.