If you haven't read any of the Eisenberg's books, you should at least read the blog. Actually, go buy the books. Especially if you are going anything with eCommerce.
Andy Beal's "Pilgrim's Picks" will keep you coming back again and again.
This Google insider always has something valuable to say.
Mobile is the new frontier, or as Mobile Storm puts it in their new campaign: SMS or DIE.
From Aaron Fallow and friends, the folks who brought us the Online Marketing Summit. Keep your eyes on this one; they are about to launch the most comprehensive resource for online marketers.
Information broken down by search engine.
Aaron Wall is likely the most revered SEO expert in the community.
You can't forget the name, and you shouldn't forget to read it. It's one of the best.
A vast, well-organized and reliable resource.
Index up to 500 pages free. No sign up necessary.
A comprehensive toolbar.
The best.
A handy little add on. The downside is that it isn't compatible with FF3 yet.
One of the best.