Must-use WordPress plugins?

I have a very big and heavily modified Wordpress installation for my start-up (link in signature).

For speed, I like: WP-Minify and W3 Total Cache - But I also spend a lot of time refining my pages to keep them fast At the end of the day, every site has unique requirements that results in a lot of manual work that plugins aren't capable of. Just get your project going, keep learning, keep looking at the source of each page and eliminate large scripts, useless CSS, etc.., and soon enough you'll have something that is fast.

Thanks for your useful post. I'll keep this in mind.

Any more suggestions please?

Hey David, a MUST have SEO plugin is the SEO by Yoast plugin, I don't know where I would be without it. It allows you to specifically target keywords to imrpove your SEO, and makes suggestions on tags, images, etc to make it quick and easy.
If you are interested in getting your blog to run on complete autopilot (it is possible) I highly recommend reading this post about a very cool plugin that has been running all of my blogs for years:
AutoWordPressBlog | WordPress Robot

Because there is NO such thing as "must-use" plugin. Whoever tells you otherwise - is a liar.

Every blog is different, every site needs different additional features (and plugins).

I've got a bakers dozen that I use in all my blogs:

1. Akismet
2. Bad Behavior
3. Easy Contact
4. Google XML Sitemaps
5. Login LockDown
6. TinyMCE Advanced
7. Tweet, Like, Google +1 and Share
8. Ultimate Plugins Smart Update Pinger
9. W3 Total Cache
10. WordPress SEO plugin by Yoast
11. WP-DBManager
12. WP-Optimize
13. WP Google Analytics
    

the two essential plugins that I use are the stat counter and wprobot3 plugins. Stat counter is always giving a review of the visitors to the site and wprobot3 constantly builds articles and I review those articles and reconstruct them and publish them.
there are hundreds of plugins available, it all depends on the person and what exactly they want for their blog and what works for their blog.

Akismet - best guard against comment spam for WordPress blog!

WordPress Database Backup - This plugin is a life saver when things go wrong! It allows on-demand backup of your WordPress database.


Search Engine Optimization (SEO)

WordPress SEO by Yoast - Yoast's all in one SEO solution for your WordPress blog: SEO titles, meta descriptions, XML sitemaps, breadcrumbs & much more.

All in One SEO Pack - Out-of-the-box SEO for your WordPress blog. If you are using the "WordPress SEO by Yoast" plugin then don't install this one.

Google XML Sitemaps - This plugin generates a XML-Sitemap compliant sitemap of your WordPress blog. This format is supported by Ask.com, Google, YAHOO and MSN Search.


Blog Statistics Related

Google Analytics for WordPress - This plugin makes it simple to add Google Analytics with extra search engines and automatic clickout and download tracking to your WordPress blog.

WordPress.com Stats - Tracks views, post/page views, referrers, and clicks. This plugin requires a WordPress.com API key to function.


Caching Plugin

W3 Total Cache - The fastest and most complete WordPress performance optimization plugin. After you use the w3 total cache plugin you won't go back to using WP Super Cache.

WP Super Cache - WP Super Cache is a static caching plugin for WordPress. It generates html files that are served directly by Apache without processing comparatively heavy PHP scripts. By using this plugin you will speed up your WordPress blog significantly.


Blog Security

WP Blog Security Tips - This is not a plugin but all the tips mentioned here should help you securing your WordPress blog.

LoginLockdown - Login LockDown records the IP address and timestamp of every failed WordPress login attempt. If more than a certain number of attempts are detected within a short period of time from the same IP range, then the login function is disabled for all requests from that range. This helps to prevent brute force password discovery.


E-commerce, Paypal Donation and Payment

WordPress Simple Paypal Shopping Cart - is a very easy to use plugin that allows you to sell products or services online in one click from your WordPress blog. Very useful when you want to sell eBooks or digital products from various posts and pages and need a WordPress Shopping Cart solution.

WP Easy Paypal Payment Accept - This is a very easy to use WordPress plugin to Accept donation or Paypal payment for a service or a product in one click. Handy when you are trying to put a customized donation option in the sidebar of your blog.

WordPress eStore - This plugin provides a complete solution to sell digital products securely from your wordpress blog.


Membership Plugin

WordPress eMember - WordPress eMember is a membership plugin that can turn your existing or new WordPress site into a membership site easily.


RSS Subscription Related

FeedBurner FeedSmith - 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.

Add to Any: Subscribe Button - Helps readers subscribe to your blog using any feed reader.

Category Specific RSS Menu - A simple WordPress plugin to add category specific RSS subscription menu into your posts, pages, sidebars. Very handy when your blog covers multiple topic from non related subjects. This plugin was developed by me.


Contact Forms Related

Contact Form 7 - Contact Form 7 can manage multiple contact forms, plus you can customize the form and the mail contents flexibly with simple markup. The form supports Ajax-powered submitting, CAPTCHA, Akismet spam filtering and so on.

cforms - cforms II is the most customizable, flexible & powerful ajax supporting contact form plugin.

WP Contact form - WP Contact Form is a drop in form for users to contact you.


Social Networking

Sociable - Automatically add links to your favorite social bookmarking sites on your posts, pages and in your RSS feed.

Share This - This is a very useful plugin that allows your visitors to share a post/page with others. Supports e-mail and posting to social bookmarking sites.

Fat Free WordPress Social Share Buttons Plugin - This is a very simple and FAT FREE share button plugin that adds Google plus one, Facebook and Twitter share buttons to your blog posts.

For Google Adsense

Simple Google Adsense insertion - Easy to use WordPress plugin to insert Google Adsense to your posts, pages and sidebar. This plugin was developed by me.

Adsense-Deluxe - Place Google AdSense ads in your WordPress Posts. Capable of handling complex adsense management.


Other Very Useful Plugins

Simple Tags - This is one of my most favorite plugins. It makes my WordPress Tagging life so much easier. It helps with Auto completion, Suggested Tags, Tag Cloud Widgets, Related Posts, Mass edit tags.

Executable PHP Widget - Like the Text widget, but it will take PHP code as well. Very handy for inserting custom 'php', 'html', 'javascript' in the sidebar.

WordPress Newsletter subscription - Creates a simple form to collect subscription requests to newsletter software managed mailing lists.

WP-Polls - Adds an AJAX poll system to your WordPress blog. Allows you to easily include a poll into your WordPress's blog post/page.

No Self Pings - This plugin does exactly what the name suggests.

Exclude Pages - This plugin lets you manually exclude WordPress pages from the navigation menu. Comes in handy when you are trying to create hidden pages.

WP Smush.it - This WordPress plugin reduces image file size and improve performance using the Smush.it API within WordPress. Everytime you upload an image to your media uploader this plugin will automatically compress the image without losing quality!

I like the All-In-One SEO plugin!

One more BS "must have" plugin list - and the thread will be gone! Deleted.

All in one seo plugin and xml sitemap are great plugins, but everyone has different requirements, so that;s why people have different recommendations. You should test yourself to see which one works best for you!