Lots of articles cover the basics, again this is an article that acts as “SEO flypaper” and rounds out the rest of the articles. My recommended strategy is to write focused, more “serious” treatments of SEO data collection.
My current favorite tool is google analytics. The “top 20 keywords” is ironically its weakest point, but the site overlay is wonderful. I used it to do path analysis for the purpose of identifying poor site layout. What does that have to do with SEO? A lot. Many of the same factors that make good user navigation (placement of key links, the words you use for them, etc) appear to please the google gods too. The new Links tab is very cool – you finally know who’s linking you. I’ve noted that many of my site’s backlinks are from “favorite links” in blogs. It’s worth keeping your eye on them. In fact, I started a separate thread Blogger Favorites just to keep track of the really good ones (not all referring back to my site, oh well).
The diagnostics on google analytics are pretty good. They’ve found broken links post-migration in the forums that I missed. Sure, I know, they’re only internal links…
I tend to pay the most attention to the organic referrals by source. The percentages hold stable within a few points and getting them to budge even 2-3% consistently demonstrates real progress. If your site runs contests and such, it pay attention to the visitor patterns. For example, it’s best to start a contest on Sunday if your main traffic day is Monday. Not SEO stuff per se, but just smart webmastering.
The overall purpose of this article is to highlight a few tools and recommend practices for collecting data to demonstrate that your SEO efforts are working (or not).