Shameless plug:

I wrote an Android app a few months ago to help learn/maintain Spanish.

http://www.appbrain.com/app/com.h4labs.free.spanish_vocab

I've been studying Spanish for several years, including 10 weeks in Guatemala. It's easy to get rusty and I always need a refresher so I wrote this app. Gonna add more grammar and hopefully turn it into a "real" app, including versions for French(started), German, etc.