You have essentially three choices: synchronize with the Palm Desktop using the Palm Desktop, synchronize with iCal and the Address Book using iSync, or synchronize with iCal and the Address Book using the three conduits provided by Mark/Space with the Missing Sync.
While it's free, the Palm Desktop will not be updated by Palm for use with future Palm OS devices, and is limited to use with the Palm contact and calendaring applications alone. While iSync is also free, it barely gets the job done with iCal and the Address Book.
Only the Missing Sync for Palm OS supports categories and groups [including calendar color indicators] and offers iPhoto, iTunes and AvantGo synchronization, USB, Bluetooth or network synchronization where they are supported by your device, the creation of conduits 'sets' and many, many other features. There is absolutely no comparison between the applications: the Missing Sync is in a class of its own.
Read about the feature set here, and it should be clear that it's not just another way to synchronize your Palm device:
http://www.markspace.com/missingsync_palmos.php