Show your solidarity with the brave people of Iran and turn your twitter avatar green.
I think that this can qualify as an opportunity to help the oppressed people of Iran by mounting 5GW-type campaigns to help them out by showing them that we are aware of their struggle.
Other things you can do to help these tweeters out is to change your time zone in your twitter settings to +3.30 GMT (the time zone of Iran) and to change your location to Tehran to give the Iranian Security Forces more Twitter Accounts to go through while they try to track down legitimate Tweeters from Iran. (Hat Tip to Paul Van Heden on Facebook)
RT (ReTweet) as many of the items you see posted with #iranelections #Tehran and other trending hashtags...also with an eye toward giving them too many targets to choose from.
Boing Boing has a Cyber War Guide that is an excellent resource. (Hat Tip @PeoriaPundit)