Sitetrail.com offers a wide range of competitive intel stats abouts a competitors website in a well presented fashion bit.ly/quWERk. Various intel is offered under the following categories: SEO Analysis, Visitor Analysis, Traffic Analysis, Revenue Analysis, Content Analysis, Link Analysis, Hosting Analysis, Domain Analysis, Server Analysis, Color Analysis (never seen that one before!!!), DNS Record Analysis, and HTTP Header Analysis. As you can see a pretty comprehensive selection. Unfortunately, I could find any ability to compare multiple competitors at once. Nonetheless, a decent effort at a one-stop-shop.
When a competitor site you're tracking changes, did you ever forget what the old version looked like? The Way Back Machine will help you out in many cases bit.ly/mWVpCE. While not all sites are tracked, many are. This tool could also provide you with a better idea of how changes to a competitor's site have trended over time, which might give you a better guess at where they're headed in the future.