I assume you still have all your stuff and the iPhone backup on the PC.
First turn off auto sync when plugged in for iTunes.
Then click transfer purchases to get your apps transferred.
Sync your Contacts (with Address Book), Notes (with Mail), and Calendar (with iCal). If you ever get a message asking you to merge, pick merge.
On your PC, consolidate your iTunes library. Copy the music folder from your PC to the Mac user/Music/iTunes Music directory. Your ringtones will also be in there and any movies.
Copy any pictures folders that you used for syncing from your PC to the Mac.
Sync the ringtones, music, pictures, and movies.
That should do it. You'll be transferred after all that. Anything goes wrong, just restore from the PC.