Adobe has put up Lightroom 2.0 as a public beta. This version includes 64-bit support and some great tool enhancements. John Nack has a good intro to this version, and is updating his blog post with new information as he finds it.
If you own a current copy of LR, you can keep your beta install running until Aug 31. All others get a 30-day unlimited preview. Be sure to check out the known issues (pdf) because this is a beta, after all.