I'll have a separate post at some point about technical blogs that I read, but since I'm a relative n00b at being a manager (I had a matrix-y job with a management component for a year, and 5+ years as a team lead, but this is my first stint with "the M word" in my title), I've been concentrating lately on trying to learn as much as I can about good management practices.
Some resources that I've found helpful:
Joel on Software -- Part technology, part management, all good reading. Joel and I part company on the subject of agile project rooms (he hates them; I see them as a best practice), but there's a lot of good advice there, especially about hiring and retention.
Rands in Repose -- His Management Cheat Sheet is a great introduction, and the rest of the blog is well-written and packed with neat insights.
Manager Tools -- Now we've left the technology world entirely in favour of the world of management. This podcast is a gold mine, and they've probably forgotten more about good management than I've learned yet. Some parts are less relevant in a specifically technical setting (in particular, the one-page resume they recommend absolutely won't cut it for an individual contributor position in software), and some can stand some adaptation in an agile environment like we have, but it's generally great stuff.
Marc Andressen is always a fun read. He goes into the economics and business needs of startups more than into line management.
Other recommendations for good resources for new managers would be gratefully appreciated!