Akismet: Top of the list, both metaphorically and alphabetically, the Akismet plugin stops me and my site being flattened by spam.
Contact Form to DB Extension: this one belongs alongside the one above. Basically: I lose email. So the contact forms can also write to database and keep all the responses in one place for me :)
Disabler: I use this plugin to turn off a couple of things including those awful quotes that wordpress puts in if you take your eye off it for a moment!
FeedBurner FeedSmith Extend: I've never tracked the traffic on my feeds (and as I type this, I realise I haven't actually checked the stats on the feedburner accounts yet!) but I have always thought I should, so I moved my feeds to feedburner and this plugin helps wordpress present that coherently.
Google Analytics for WordPress: plugin to (allegedly, I haven't paid much attention) do more than just throw your analytics code into your template.
Google XML Sitemaps: I have never had a proper sitemap and was advised that I need one, so now I do. Wordpress has a plugin for everything :)
Orderli: The links in the footer of this site are pulled from different categories of links in wordpress and while there are options to sort by different metrics, none of them were quite right! So I added this plugin to enable me to re-sort them.
PluGeSHin: I picked this very new plugin over WP-Syntax purely because it is triggered by the same markup as the GeSHi plugin in serendipity (my old blogging platform) was. With almost 700 blog posts, avoiding that kind of migration was a big plus point! I am having problems with this plugin though, it has "eaten" all my XML code snippets, so I may yet migrate away from it.
RSS Footer: This one adds a footer onto posts that get published on feeds, just a chance for me to say who I am and to link back to this site (since my content gets plagiarised fairly often, at least there's something for people to find the original). I like it because it doesn't put anything into the posts - I can turn this off or change it as I go along.
SlideShare: This plugin takes a slideshare URL and replaces it with the embedded presentation found at that URL. I use this extensively to display my slides on the resources section of the site to show slides from recent conference talks.
WordPress Database Backup: download a mysql dump file from your wordpress dashboard. Not sure why I need this, other than I think anything that stops me logging into live servers is probably a good thing!
I realise now that there are 12 plugins in this list - I must have installed one while the post was in draft! Now I've shared mine, I'd like to hear from you. Is there a plugin you couldn't live without? Or one here that's new to you? Please leave a comment - I'm newish to wordpress so I'm really interested to hear from others.