There were a couple of rumors floating around about an upcoming Windows Mobile version which follows current Windows Mobile 6 and during today's Möbius conference, Microsoft gave us a sneak peak of it. While it was shown in its full flavor (as available today, I'm sure we will see some further changes until it becomes available), Microsoft asked not to talk about details or features yet. What I'm allowed to say anyway is, that the next Windows Mobile version is an update rather than an upgrade. So don't expect anything groundbreaking new but useful enhancements and changes.

Availability for ODMs is anytime Q1 2008 and therefore, commercial availability can be expected during Q2, latest Q3 next year.

UPDATE: Because I got a couple of E-Mail (please use the comments bellow instead): Yes, it was shown on a current device but this doesn't matter. Microsoft has to use current devices to do their development of upcoming releases; would be too much to develop new hardware just to develop a new OS version (or updates) after. So the good part is that there are serious chances to see this Windows Mobile update available for current devices too (as it happened in the past with other Windows Mobile releases) but as always it's up to the ODM, OEM and carrier if these updates are offered or not.
And no, Microsoft doesn't showed what we know a "Photon" or "Windows Mobile 7". Again, it's an update to what we know already, not a groundbreaking upgrade even if I have to admit, that this update adds functionalities, smaller and bigger, you might have heavily awaited - or not.
Q1-08 isn't that far anymore so I expect we will get something official in the not too far future.

Cheers ~ Arne