SVG has been in development since 1999 and in 2010 we can say that all major modern web browsers except Microsoft Internet Explorer, support and render SVG markup directly. The Internet Explorer 9 beta supports SVG.
Protovis Great for data visualization. It only works in browsers that have native SVG support.
Raphael It's a good starter library, easy to do a LOT of things with SVG quickly. Well written and documented. Lots of examples and Demos. Very extensible architecture. Great with animation.
But note that there are ways of expressing things in SVG that are not possible in Raphael. There are no "groups". This implies that you can't implement layers of Coordinate Transfomations. Instead there is only one coordinate transform available. If your design depends on nested coordinate transforms, Raphael is not for you.
It supports Firefox 3.0+, Safari 3.0+, Chrome 5.0+, Opera 9.5+ and Internet Explorer 6.0+.
jQuery SVG Well written and documented. Lots of examples and demos. Supports most SVG elements, allows native access to elements easily.
It only works in browsers that have native SVG support.
SVG Web It uses flash to render in non-SVG compliant browsers.