2. Ear Trainer Lite

On iTunes: itunes.apple.com
Price: Free
Ear Trainer Lite is a great educational tool. It's designed for musicians, music students, and anyone who's interested in improving their "musical ear". The app offers exercises covering intervals, scales, and chords. The LITE (free) version offers 32 different exercises. The full version ($6.99) offers 230 exercises. Try out the free version and if you like it, upgrade to the full version!