the list I use, taken from a toplist a long time ago
Essential
1. Google Analytics for WordPress
Developed by yoast, this is an essential one for hooking your WP site into Analytics.
2. WordPress SEO by Yoast
I thought that the All in One SEO Pack plugin was the best SEO plugin until I tried Yoast?s WordPress SEO plugin. It actually previews your title and meta description tags and lets you know if you?ve missed an element in your post based on your targeted keyword phrase. It also adds sitemap.xml and Google, Yahoo! and Bing site verification functionality! Joost ?Yoast? de Valk rules.
3. Mobile Edition
WordPress Mobile Edition is a plugin that shows an interface designed for a mobile device when visitors come to your site on a mobile device.
4. Widget Logic
This will allow you to display widgets on specific pages using a single sidebar. Without it, your widget would display on every page or post using that sidebar. For example, you might want to have a location map on every page EXCEPT the Contact page.
5. WP Database Manager
Your database is your heart ? treat it right using this one. Allows you to schedule an automated backup via email, repair, optimize and more. Just get that pesky .htaccess move right to remove the warning message.
Useful
6. Maintenance Mode
Develop your blog while putting a ?Coming Soon? message up to the public. Very useful.
7. CryptX
Email harvesters are the scourge of the Internet. Just add an email address to a post or page and let this one automatically encrypt it so the address can?t be recognized by those harvesters.
8. Kadom 125 Banner Ad Manager
Manage your 125 x 125 pixel banner ads using this and see how many click-throughs each one gets, useful feedback for the advertisers. Set up multiple campaigns and locations!
9. Update Notifier
I find this one useful for sending an automatic email to the client to let them know that there is an update to WordPress. This keeps them on their toes and invested in their blog. It keeps sending emails until it gets updated!
10. Social Profiles Widget
Add your social profiles using this neat sidebar widget. Has some sweet icon options too.
11. Post Expirator
With WordPress, you can schedule a post by putting a future date in but you can?t bring it down. Use this one to do just that.
12. Duplicate Post
You know, small can be beautiful and this one just saves time! Have multiple posts? Use this to quickly duplicate an existing one that took you an hour to create then off you go.
13. My Calendar
Seems to be the best WP calendar on the market today, has great customer support, and worth a donation. Allows location setup to save time, repeating events, and more!
14. AddToAny
Social sharing is essential these days to why not add this to every post.
15. Shopp for eCommerce
A solid eCommerce plugin with great support and plenty of options.
Don?t forget to make a donation to these fine plugin developers.