Userscripts.org – Universal Repository: Here’s a site full of Greasemonkey scripts for about everything you could ever imagine.
I like this one, that automatically switches all Amazon affiliate links in the page you’re viewing to your own affiliate ID. Sneaky.
This one for Blogines continually checks your feeds in the background via the API, and reloads the page whenever it detects something new.
This one adds a Bloglines box in GMail.
But there can be no doubt that this is the best one: it simply adds large pictures of Jakob Nielsen to the background of every single page you browse. Truly, what could be better than this? Can I get one for Spolsky too?