1. Askimet
http://www.akismet.com/Best anti-spam plugin for wordpress.

2. RSS redirector to Feedburner RSS http://www.orderedlist.com/wordpress...burner-plugin/
Essential plugin if you use feedburner. You should also see significant rise in readers.

3. Wordpress Google Sitemap Generator http://www.arnebrachhold.de/2005/06/...rator-v2-final
Good for SEO.

4. Adsense Deluxe
http://www.acmetech.com/blog/adsense-deluxe/
Adds google adsense to your posts and makes sure you dont display more than 3 on a page.

Add some more if you can think of them