Specs, primers, validators, stuff like that

The CSShark Answers FAQs — Martina Kosloff has compiled a pretty good FAQ on CSS. Worth your time.

css/edge — From the mind of Eric Meyer comes this great little site pushing CSS to the edge. It is, in his words: “intended, first and foremost, to be as relentlessly creative with CSS as we have been practical all these years. It does not exist to present or explain safe cross-browser techniques; in fact, almost the opposite. The goal here is to find ways to make CSS live up to its fullest potential, with only minimal regard to browser limitations.”

websitetips.com CSS section — Literally a ton of links to CSS resources from all over. A better set of links than this one by far.

Style Sheet Reference Guide from webreview.com. — Eric Meyer’s excellent resource, including the justly famous browser compatibility charts. It’s a bit dated (I wish it included Opera 5 and more of CSS2) but still an excellent resource.

CSS School from w3schools.com. — A whole lot of information, references, and examples.

Cascading Style Sheets, level 1 Recommendation from the Web Design Group. — This is the spec (really a rec) folks; can be very helpful if you learn how to read it.

W3C CSS Validation Service — Download a CSS validating app, give it a URL, or cut and paste your CSS here for the ultimate in CSS Validation services.

The Layout Reservoir from BlueRobot. — A resource much like this page with beautiful CSS layouts for you to steal.

Agitprop — Todd Fahrner’s collection of CSS writings, tests, and treatises. Good stuff.

CSS Pointers Group — A great resource full of information and links to other resources on CSS. Some of it is a bit dated (but what isn’t in today’s modern age?), and they are all down on multi column layouts, but still a must visit.

Eric Meyer’s CSS work — The author of the O’Reilly CSS Definitive Guide, Eric has done an amazing amount of writing and work on CSS. One highlight: his frame set views of the W3C’s CSS references.