Adobe have released Lightroom 2 including many new feature:
Local adjustment brush
Enhanced organizational tools
Multiple monitor support
Flexible print package functionality
Streamlined Photoshop CS3 integration
Enhanced output sharpening
64-bit support for Windows® and Mac OS
There's more detail here
and in the press release here
I know a lot of people have been waiting for multiple monitor support but to me the most important new features are the improvements to local adjustments and, in beta form, support for camera specific profiles available to download here
. The custom profiles are designed to emulate the manufacturer’s own conversions and picture styles.
It's also well worth reading this article
for an extremely detailed list of the new features.