Free SSL and much more webmaster stuff for your website
A great html/css/js sandbox
Great online tool for compressing large picture files to smaller files without too much loss of quality
CSS3 has some new values for sizing things relative to the current viewport size: vw, vh, and vmin. It is relevant to bring up now, because it's shipping in Chrome 20 (canary at the time of this writing). And not behind a flag, it just works. Production usage isn't quite there, but it will be soon enough.
Great list of symbols and explanations, Check it out!