Which browser extensions (if any) are people using to check sites?
I seem to remember you being a fan of SEOmoz from other posts, so you'd probably value their
Mozbar (currently more extensive data available via the firefox version, but they're releasing [or have released? I'm not sure] an updated Chrome version to match the functionality).
Is there anything specific you're looking for? Between the seobook and seomoz offerings you have most the basics available at a glance, throw in a developer toolbar and something like firebug and you're probably set for most of your needs.