I use Snow Leopard Server to sync Calendar and Address Book across Macs and iOS devices and VPN to access the server when outside. The downside is some places VPN is blocked.
I've experimented with Google instead. It seems to do fine with calendars but falls flat with the address book because it won't handle the categories (subfolders for different people).
iCloud is really a wait and see. Potentially it could be the best choice. It's coming out soon so defer your decision! In any case I really can't see buying a Mac just for a calendar server.