A couple more golden SEO tools I found recently:
Google Link Popularity Analysis Tool - Very-detailed link popularity tool that analyzes your backlinks (including their IP, pagerank, and number of incoming links), as well as a nifty backlink analysis tool.
Google PR Lookup - Bulk PR lookup tool which features a "real" pagerank tool (supposedly uses Google XML to retrieve the "real" pagerank, and not the visual toolbar PR bar).
MSN & Yahoo Keyword Tracker - I've seen a couple Yahoo trackers, but the MSN tracker is a new one.