There are 11 powerups. All eleven are listed on the FUN RUN page, along with a brief description of what they do, whether (and by whom) it has been found, and whether it has been activated. For longer descriptions, click the name of the powerup. They're pretty funny, actually:
http://www.democraticunderground.com/discuss/duboard.php?az=funrun#powerupsWhether anyone finds a powerup is random. Whenever you move any candidate on the FUN RUN page, there is a chance that you will find a powerup. If you find one, you will get a notification telling you which powerup you found, and how to activate it. You don't get to choose which powerup you find, but you do get to choose which candidate(s) the powerup will affect.
If you are the person who found a particular powerup, then a button will appear on the powerup so you can activate it. You do not have to activate it immediately, but you need to activate it before the DU fund drive takes in 900 donations, or else you miss your chance.
One more thing: We set it up so they cannot be found after the fund drive takes in 900 donations. If you're waiting until after 900 donations to move your candidate without fear of your moves being undone by a powerup, you are going to miss your chance to (maybe) find one. There are still some powerful ones left.