Just bought a loop pedal.. its a pedal that loops anything you've played, and often comes with some simple drum tracks. Although it doesn't sound much, its a great way to practice riffs as you can change the tempo of your recording, and playback your guitaring. It's also a great way to compose riffs and songs, for example by trying out different riffs with chord progressions.
Check out this example, using a simple A E D E progression:
Here, i tried starting the song with a clean riff. I then built it up with some open chords, followed by some muted notes with delay. I added some distorted chords, and ended off with an improvised solo.
Here's another example: