The most well-known is the buff Livestrong wristband, popularized by Custom Wristbands Lance Armstrong.
One type of wristband is also avowed as a sweatband, and is usually fabricated of a towel-like terrycloth material. These are usually used to wipe sweat from the forehead during sport, or as a badge or fashion statement. A practice common in mid-eighties punk subculture was to cut the top off of a sock and fashion the elastic into this type of wristband.