I found a brief guide to helping Iranian bloggers via Twitter. Check it out here, and if you're on Twitter, consider reading it.
The three most useful and easiest suggestions:
Don’t blow their cover! If you discover a genuine source, please don’t publicise their name or location on a website. These bloggers are in REAL danger. Spread the word discretely through your own networks but don’t signpost them to the security forces. People are dying there, for real, please keep that in mind.
Keep you bull$hit filter up! Security forces are now setting up twitter accounts to spread disinformation by posing as Iranian protesters. Please don’t retweet impetuosly, try to confirm information with reliable sources before retweeting. The legitimate sources are not hard to find and follow.
Help cover the bloggers: change your twitter settings so that your location is TEHRAN and your time zone is GMT +3.30. Security forces are hunting for bloggers using location and timezone searches. If we all become ‘Iranians’ it becomes much harder to find them.