Mobile-review has a great, er, review of the upcoming version of Windows Mobile, currently codenamed Crossbow. As they say, don't expect a revolution just yet - that'll come with the next version, Photon.
In any case, there's some notables in there you'll want to check out. Here's the spoiler, though: you get more eye candy, better button support, built-in VOIP, and better integration with MS Exchange 12
*Nevertheless, the brand-new operating system could be called “Windows Mobile 5.0 Second Edition” for it lacks tons of all-new features and total system revamp as in the case of Windows Mobile 5.0. *