Rush: Limelight (don't care what you think about Getty Lee's voice, it's a great riff - If I pick up the electric, I will almost always run through this riff for some reason - maybe lame, but I can test the sound on any guitar/amp with this riff and know how most other songs will sound in just a few seconds)
Ten Years After: I'd Love To Change The World (one of the first riffs I HAD to learn, and it sounds good on an electric or acoustic)
ETA: Just picked up the guitar and forgot the one I almost always play - Van Halen: Drop Dead Legs.
You all probably just guessed (accurately, I might add) that I stink on the guitar. Maybe someday if I practiced more and didn't have so many broken fingers I would get to a stage of less stinkage, but unlikely I'll ever be great at it. I just enjoy it, and don't worry too much about how I sound. Plus, I bought my house from a drummer and have a sound proof room to practice in, so the family isn't injured by my lack of talent.