WPBeginner has a great writeup of what we can look forward to in WordPress 3.0. Of course there is the merge of WordPress MU into WordPress, the awesome Woo Navigation menus, a new default theme, and custom post types just to name a few. WordPress 3.0 has a tentative release date in early May but that could be pushed back if any major breakage occurs during the beta cycle.
Now you’ll have to tell me what is it your most looking forward to in this version of WordPress. For me, it’s the new navigational menu system.