Its a musical challenge... find as many different groups/individuals in this image as you can (click on the image for a larger view). I can't remember the total amount, but there are certainly more than 50. Guns and Roses, Mathcbox 20, Queen and the Rolling Stones are all there. How many can you see? Some are easy, many more are a little more problematic.
Once you start, you'll be hooked. Friends will be intrigued. It's good fun. Let me know how you go... How many did you find?