The Spaminator. Catches a ton of spam. I’ve only noticed one false positive so far out of hundreds of spam comments.
The dofollow plugin. Because I am really fairly good about getting rid of spam comments that slip through (and I expect less and less to appear due to the Spaminator), I like that this plugin will remove the default nofollow tag added to urls in the comments in version 1.5 of wordpress. I think the nofollow thing is a bit lame in any case.
I just installed this contact form plugin.
I really like the way it is so easy to use plugins in wordpress!
Here are some pages where you can find plugins to customize your wordpress blog: