Here’s a decent tool for finding relevant stats for competing websites, your own websites, and sites you’re looking to buy. It’s also good for potential domain buys.

Click: XinuReturns

It checks PageRank, Backlinks, Indexed Pages, Rankings, Social bookmarking coverage, and other stats.

While there are some SEO plugins that carry some of this information, this site has a more extensive list of stats than many plugins out there.