#1. Plant maintenance. You're plant can always benefit from some simply grooming--clean out the dead leaves, water it, place it in a good spot for sun, etc.
#2. Organize. Whether it be your post it collection, pens, or stocking up on supplies, your desk and desk drawers always need to be organized.
#3. Update your Facebook status. Or write on your friends wall.
#4. Play games online. Try Yahoo! games, or Miniclip. Just make sure to alt+tab over when your boss walks by.
#5. Look at your blogroll, and others. Not only can you learn new recipes, random facts, or local events, it's bound to waste a good 10 minutes or so.
#6. Check all your e-mail accounts. Maybe even e-mail that friend you've been meaning to e-mail for the past month. Now's a perfect time to do it.
#7. Take a walk around the office.
#8. Refill your water, make some tea/coffee, or grab a snack.
#9. Catch up with a co-worker. Now's the time you want to hear all their stories. The more questions you have, the longer the conversation will last.
#10. Check your bank account balance, pay bills online, or put books at the library on hold.
....more to come. Additions are welcome too!