June 30th of this year, Apple pulls the plug on MobileMe. Many of the features of MobileMe are available for free as part of iCloud, and if you’re able to switch to iCloud, I recommend it. Many users, however, are using Macs that won’t be able to support iCloud for syncing contacts and calendars.
For these users, as long as you’re using Leopard (at least version 10.5.3) you can use a Google account for free on your Mac and your iOS Device. To configure this, you can just open Address Book, go to Preferences, then check the box labeled “Synchronize with Google.” After signing in with your gmail (or Google Apps) account, your address book should start to sync with Google. This method is significantly slower than iCloud, in my experience.
For iCal, you can do basically the exact same thing. MacWorld posted a good roundup of the best ways to get Google to sync reliably with iCal. Read their article here.