Hey Sandy,
Another WordPress user.... GREAT!! You're gonna love it. In my opinion the must-haves are....
All-in-One SEO Pack - It allows you to create separate <title> for your meta title tag. The WordPress default is the title that's in your post is the same title in your <title> tag.
It's nice to be able to differentiate them because I try to use keyword-focused titles for the <title> tag (for search engines) but I often want my blog title to have something more catchy for RSS readers, BlogRush, etc.
http://wp.uberdose.com/2007/03/24/all-in-one-seo-pack/
Google XML Sitemaps - creates a sitemap on-the-fly after every post and submits them to the appropriate engines.
http://www.arnebrachhold.de/projects...nerator/#P18DL
Custom Query String - When you search categories and archives on WordPress, the default is to only show one post. I hated that. If you use this plugin, you can specify how many results are returned when someone clicks on a category in your archives, search by date, etc.
http://andybeard.eu/?dl=3
http://www.transycan.net/
Those are my faves. Others feel free to chime in with yours.