A heavy bout of googling turned up only one alternative to Spanning Sync and a couple of contenders for full Outlook-GCal syncing. I will keep looking.
BusySync (or it’s bigger brother BusyCal) looks like a good alternative to Spanning Sync; it’s cheaper ($50) but cannot sync contact details. So far, that’s all I have found. Any other ideas?
Outlook-GCal is a richer field: the previously mentioned SyncMyCal (if you don’t mind a virus), OggSync, gSyncIt, KiGoo, Plaxo and many more.