Mine is Akismet, for obvious reasons, even if it takes a while before spammers find a new blog (usually) and the first ones that I use I guess would be others...
I have a small shell script that automatically installs about 10 plugin-ins, including Akismet, all-in-one-SEO, google sitemaps, wp-cache and others. I run this every time I set up a new blog.
sitemap plugin first for my new sites helps SE bots for fast crawling of my new site, and that is an advantage
When using wordpress, the first one I install is a site map generator, then I add the output file to my google webmaster tools. My wordpress "blogs" act as portals to my forums. Comments are disabled on all articles and a link is provided at the bottom of the article to the forum thread where the article can be discussed. Since I do not allow comments on my blog, there is no need in spam control plug-ins.
Interesting. So Akismet, All-in-one-SEO, and sitemap generator are the first ones in general... Good to know... Thanks!
That small shell script developed by you or available free for everyone Can you give me its download link please ?? DON.
all in one seo is surely one of the best and a must have, askimet comes as default i guess, so its the first
Just to be different, I'll say WP Automatic Update, but the ones everyone else has listed here are all definite installs on the same session...order really doesn't matter to me.
I install the WP-Backup, it is probably the most important plugin next to Askimet IMO. That's always been the second plugin I install.