Good point, weegillis. I'll expand on mine a little, too.
I use Quirk SearchStatus, a FireFox add-on (you can check it out here:
SearchStatus | Firefox SEO Toolbar Extension). These are the standard drop-down tools:
Highlight NoFollow Links
Link Report
Metatags
Show in Archive.org
Show Whois (selectable for who-is, who.is, DomainTools or DNStuff)
Show Robots.txt
Show Sitemap.xml
Show keyword density
Highlight keyword
Show indexed pages (G, Y, M or all)
Show backward links (page, page external only, domain or domain external only)
It also will display PageRank, Alexa, Compete and mozRank, any or all of them.
It's not the end-all, be-all, but it's quick and handy, and will at least show you enough to let you know if you want to dig deeper, with a better tool.