Ok, I'm sure the last thing you need is yet ANOTHER blog to add to your aggregator, let alone a list of blogs, but I can't help but pass along MarketingSherpa's 10 Best Blogs for 2005.
If the whole list is too much, here's the condensed version:
Best blogs on the topic of general marketing and advertising
I'll do my best to pass along the most relevent posts for librarians.
Seth Godin also has a blog that relates to his newest book, All Marketers are Liars (5 page excerpt here). The blog's hilarious! His book, by the way, is at the top of my "to read" list, so I'll give you a run-down of "what librarians could learn from this" once I finish it. If any of you have read it, let me know what you think!