My plugin Automatic Post Tagger is the best one, of course. It is so good that I am sure that they will include it in every WP installation by default when they finally realize that nobody needs Hello Dolly, Akismet and similar nonsense.
I'd say JetPack from Automattic - improves a number of features across your site including comments and speed. Also, All in One SEO and WP Backup are great.
It's not just me that really thinks that Hello Dolly stuff is all nonsense then. Must check your plugin out devtard, as i said b4, as tagging is now more important than ever b4... for me bwp site maps and a related posts plugin and I have recently been using "add meta tags" but that's about it and who knows when I might change my mind...
I could actually create a plugin that would prevent WP from installing these silly things every time it is being updated. Stay tuned. Edit: There is already a plugin which does the job, check it out: http://wordpress.org/plugins/unwanted-plugins-remover/
BulletProof Security. Really, it just adds some rules to .htaccess, but it's the first plugin I always install.
It's funny you mentioned that Ryan as I nearly put "other than a couple of security ones I have been testing/playing with" but wasn't sure enough about them, as still testing the waters and finding out stuff about them so didn't want to mention them. I only dropped "SEO ultimate" in favour of "add meta tags" a few months back and previous to that had dropped "all in one SEO" in favour of "SEO ultimate" and previous to that had dropped "Yoast WP SEO" in favour of "All in one SEO".
Funnily enough, I dropped All in One SEO for WordPress SEO. Oh, another good plugin is Head Cleaner. It's not perfect, but better than similar plugins I've used.
Head Cleaner, Spammer Cleaner, Hand Cleaner Wish if there is a Home Cleaner Plugin that i can use for my Office Room at home LOL To answer the question : i don't really have a Preferred Plugin or "Best" Plugin.. because that depend of the situation, the content, the design and the Needs of such or such plugin in my case EVERY PLUGIN THAT CAN SAVE ME HEAD-ACHE CODING is THE BEST
I like Permalinks & SEO plugins ! There are thousands of plugins which are very useful for wp blogs & increasing rapidly.
I'd recommend JetPack as well from Automattic - it has so many features that you'll probably not need any other plugins any more with just this one. Carousel and Photon and Mobile Theme are my favorite modules of all