There’s Spanning Sync for Mac (it would be useful to list which products are Mac and/or Windows as we continue):
Spanning Sync 3 - Sync iCal with Google Calendar, Sync Address Book with Google Contacts
I tried the download and it did sync contacts but not my calendars from iCal. Tech support was very fast at replying but their suggestions didn’t fix the issue and now I’ve yet to hear back. So its getting removed although I’ve read comments from others it works well. $25 pre year or one time cost of $65.
The Mark/Space product looks promising, I know in the past, they have supported these solutions on the Mac very well.