Do you have a pair of pants where the zipper seems to always fall down? Here is a quick solution that works really well. Use one of those small ball chain keychains to tether the zipper to your pants button. Simply string the chain through the hole in the zipper tab and attach the ends. Pull your zipper up, slip the keychain over the button, and button your pants. Voila!
If you find that the keychain is a little too long to keep the zipper at the top, it is easy to cut it to the desired length.