I had these made for my projects and figured some of you could use them as well. I have ten of these 30 second loops. For a good example of how they can be used, check out my demo game PinWall, by hitting that "try in arcade" button.
In this game, I change the music as you get farther into the game, as well as change music when entering a menu.
They are all in WAV format, and can be looped perfectly. They each last 30 second, give or take.