A favorite practice technique of guitarists is to play along with your idols, mentors, and teachers. Guitar Shed's "Song Jammer" lets you load in just about any audio file (Including MP3, QuickTime®, AIFF, WAV, AAC, and many more) - and jam in realtime with it.
The real power of the Song Jammer comes from its powerful features such as Song Looping - which lets you automatically repeat specific sections of a song over and over, a full equalizer, and playspeed editing - which lets you speed up or slow down the song; perfect for learning those fast solos and bridges.
The Song Jam is an essential tool for any guitarist. It's also an excellent way to painlessly learn those cover tunes.