Tracking inbound links from weblogs to just about anything, using the Technorati Anywhere! bookmarklet (a godsend).
Figuring out who else follows that new blogger on the block.
Update (Jan. 9): As Ross
reminded me in his Linkorama, Google is a good blog search engine too.
Just append "blog" or "weblog" to your search request. And (says Alf) if you don't want blogs, append "-blog".