I'd recommend the following to get started: Akismet All in one SEO WP Super Cache Contact Form 7 Disqus Feedburner Feedsmith Wordpress Database Backup Wordpress Automatic Upgrade Google Analytics for Wordpress There are many more as you know but this would be my core group to start with.
My two favorites are the "Dofollow Trackbacks 1.0" which has gotten me a lot of good traffic and "WP-Ban 1.40" which will block anybody, like spammers from using your site.
In one blog I use WP Post Columns so I'll have a newspaper like look in some posts I choose to. It's the only plugin for this that I can find that seems to work. The others don't. No fancy GUI to do your columns for you though. You have to insert short codes in your post to do it.
I have about 10. 1. All in one SEO Pack for wordpress SEO 2. Download Monitor to manage file downloads 3. Wordpress Extend Download Stat to keep track of my plugin and theme hosted @ wordpress extend 4. Wordpress Theme Demo Bar to preview my themes 5. Google XML Sitemaps for google webmaster tools 6. Wordpress Thread Comment to let user reply on comment 7. WP-CodeBox to display scripts/codes in post and i forgot what else I have