The Acid 2 Test is a holy grail of web standards support that designers wish browser maker would strive for. Basically if your browser can display this page as a smiley face, it has good standards support.
Internal builds of Safari, Opera, and Konqueror all pass the Acid 2 Test. But the first publicly available browser to pass the test is iCab 3.0 beta, for Mac OS X, currently at build 280. Really surprising considering how bad iCab used to be.