Waypath is a really nice blog search engine. The keyword search is impressive, though it's not easy to sort by date (which Feedster does well). Technorati does backlinks best at the moment, but the Waypath It! button finds much better 'similar pages' than Feedster or Google (which has itself been improving lately).
Other Waypath features include an XML-RPC API, a Buzz graph of keyword popularity over time, a bookmarklet for easy access, and plugins for Movable Type and Radio to automatically generate lists of related items for each post.
It's a shame a lot of the people involved in creating these tools aren't more willing to consolidate and work together though, so we don't have to go to five different sites to get information.
See also BlogStreet, which has had a redesign and a number of new tools added, mostly aimed at automatic RSS generation or aggregation.