I've got about $50 of credits at the Google Play store that expire at the end of Mar 31. I could just buy books, or even movies, but if you have any recommendations for apps you love, I'm all ears.

This would be for my tablet, as my phone is Windows. Mostly I use my tablet when I travel as an all-in-one device, so travel-related apps are particularly useful. The only app I've ever paid for is CitiMaps 2Go Pro, which lets you download maps that are then usable offline -- very useful if you don't want to pay for data usage.