There are scripts for thousands of sites like GMail. For handy scripts see http://userscripts.org/scripts . And for a random Top 10 scripts see http://www.lifehack.org/articles/productivity/top-10-greasemonkey-scripts-to-improve-your-productivity.html .
Me playing with GreaseMonkey for firefox

Risto's Sidebar
Invalid url 'http://[IMG]http://img15.imageshack.us/img15/7245/sidebarv.th.png[/IMG]'
I am just discovering the possibilities and will keep you updated if i find more interesting scripts
