Guitar Pro (US$7.99, universal) is a tablature player and editor with some fantastic features. In essence, Guitar Pro is a library of songs in tablature score, which reads the score in audio, while helping you play along.
When learning to play guitar, there are usually three things you need. First, of course, is a guitar. Second, you need some instruction to tell you what to play and how to play it. Third, you need to hear what you're learning to play, to make sure what you're playing sounds the way it's supposed to. I guess there's a fourth category here too: a whole lot of practice is required!
Arobas Music's Guitar Pro for iOS covers two of these bases. You bring the guitar (or bass) and the practice time and Guitar Pro will give you the instruction and the audio to practice with.
Fire up the app and you'll be presented with a sample library of included songs. Genres range from blues to classical -- easily searchable with filters. Once you've found something you like the look of, tap on it and the entire tablature for that song will open in Guitar Pro's beautiful and easy-to-use tablature player (options for rhythmic-slash notation, piano grand staff, four voices, etc. are also available).