A couple of good rundowns of the situation in Iran, since the news has been falling down horribly on the job: quettaser has one here, with an excellent collection of links, and ladycat777 has one here, with a good collection of background information as well. The Atlantic had an interesting article: Follow The Developments In Iran Like A CIA Analyst. Once you've read those, the Twitter #IranElection hashtag is essential. I can't believe I used the words "Twitter" and "essential" in the same sentence.
If you want to help, there is an excellent list of things you can do here; the most important, to my eye, is to follow the instructions for setting up proxies, as this will help the people in Iran continue to talk, to each other and to the world. Remember: do not retweet to users in Iran; their government knows about Twitter and is following, and there have been a lot of reports of arrests. The second most important thing you can do is to keep talking about this; the more people watching and talking, the greater the possibility that there might be accountability at the end of this. Talk about it: on LJ, at Twitter, in blogs, and in person. Share links and photos. Talk about those links and photos. Wear green. Talk about why you're wearing green. Try to find out if there are demonstrations near you. Contact the news providers and demand more coverage, because what we've got so far is pathetic. Keep listening, keep watching, and keep talking.
I'm sure this post needs more work, but I am running out the door in four minutes and will be gone for a couple of days, so it'll have to do.
(Ugh, I was also reminded of why I don't follow celebrity Twitters: I spent an embarrassing amount of time trying to figure out which of my flist went to Bonnaroo before looking at the name on the tweet and realizing it was an update from Steve Van Zandt. /o\)