If you ask the same question to me i would say 20 active plugins are working in my blog to keep its performance at top level though it is a bit complicated to manage them even through automatical process but i love each of them and they are really great for my blog.
Here comes the list
AdSense Integrator AdSense Integrator plugin represents a complete, simple and powerful solution to add and manage AdSense and other ads into your blog
Akismet Akismet checks your comments against the Akismet web service to see if they look like spam or not. You need a WordPress.com API key to use it. You can review the spam it catches under “Comments.” To show off your Akismet stats just put in your template. See also: WP Stats plugin.
By Matt Mullenweg
All in One SEO Pack Out-of-the-box SEO for your WordPress blog. Options configuration panel
By Michael Torbert
Calais Auto Tagger Suggests tags for your posts based on semantic analysis of your post content with the Open Calais API.
FeedBurner FeedSmith Originally authored by Steve Smith, this plugin detects all ways to access your original WordPress feeds and redirects them to your FeedBurner feed so you can track every possible subscriber.
By FeedBurner inLinks InLinks inLinks InLinks program sells links within your blog posts
By inLinks Popularity Contest This will enable ranking of your posts by popularity; using the behavior of your visitors to determine each post’s popularity. You set a value (or use the default value) for every post view, comment, etc. and the popularity of your posts is calculated based on those values. Once you have activated the plugin, you can configure the Popularity Values and View Reports. You can also use the included Widgets and Template Tags to display post popularity and lists of popular posts on your blog.
By Crowd Favorite
Post-Plugin Library Does nothing by itself but supplies common code for the Similar Posts, Recent Posts, Random Posts, and Recent Comments plugins. Make sure you have the latest version of this plugin.
By Rob Marsh, SJ
Script Enabler Enables you to use script tags in your posts without them getting horked up.
By Otto
SEO Smart Links SEO Smart Links provides automatic SEO benefits for your site in addition to custom keyword lists, nofollow and much more.
By Vladimir Prelovac
Social Dropdown Displays social bookmarks in a dropdown to reduce clutter. Remember to read the readme…
By Nicholas Kwan (multippt)
Subscribe Me Widgets that let you display subscribe links to RSS readers such as Google Reader.
By Denis de Bernardy
Subscribe Remind Give your readers a little reminder to subscribe to your blog’s feed at the end of each post.
By Trevor Fitzgerald
Technorati Tags Returns a list of technorati tags associated to the post (http://www.technorati.com/tag/). Follows the same convention of listing tags native to WordPress 2.3. the function the_techtags(); must be used within the loop.
By Will Garcia
Widget Context Display widgets in context.
By Kaspars Dambis
Widgets Reset Allows you to reset all of your widgets.
By Justin Tadlock
WordPress Navigation List Plugin NAVT Create, organize and manage your web site navigation by logically grouping your pages, categories and user’s via a drag’n drop interface. Manage your navigation lists from the NAVT Lists menu tab in the Manage menu.
By Greg Bellucci
Uninstall/Reset NAVT Plugin OptionsResetSets all NAVT created database options to their default values. This will cause any previously created Navigation Groups to be removed.
UninstallRemoves all NAVT created database options and automatically s the plugin.
WP-DBManager Manages your WordPress database. Allows you to optimize database, repair database, backup database, restore database, delete backup database , drop/empty tables and run selected queries. Supports automatic scheduling of backing up and optimizing of database.
By Lester ‘GaMerZ’ Chan
WP Security Scan Perform security scan of WordPress installation.
By Michael Torbert
Yet Another Related Posts Plugin Returns a list of related entries based on a unique algorithm for display on your blog and RSS feeds. A templating feature allows customization of the display.
By mitcho (Michael Yoshitaka Erlewine)
I would like to recommend the Platinum SEO Pack, it has more useful options than the all in one seo pack. There are more nofollow selections, additional post, page and home headers, you can nofollow all of the outgoing links on just the front page, you can add the noydir meta tag, the noodp meta tag, you can use the option for noindex on sub pages and my favorite option of all is all of the options that it gives you on each individual post and page of your wordpress blog.
Those are just a few of the things that I can think of off the top of my head. The fact of the matter is that I have used both and have found that I am in greater control of my websites on-page seo than when I was using the All in One SEO Pack.