Mark/Space, purveyors of the Missing Sync line of software which allows all kinds of non-iSync compatible devices shake hands with your Mac, has released Missing Sync for Windows Mobile version 2.5. This update includes support for a wide array of Windows Mobile 5 devices. This update also includes improvements to syncing with Address Book, iCal and Microsoft Entourage 2004.
I helped test out the alpha a couple of months ago, back when I temporarily lost my senses and *gulp* actually owned a Windows Mobile 5 device (the Cingular 8125, if you're interested). While I ditched the device because I couldn't stand the Windows Mobile OS (or: 'regained my senses'), I must say: the syncing worked well, and I would realistically recommend this app for anyone who wants or needs to make a Windows Mobile device work with their Mac.
Missing Sync for Windows Mobile 2.5 is a free upgrade for owners of version 2.0, and a $20 upgrade for owners of version 1.x. A fresh licenses costs $40.