I have a Mac and PC. I use Mailstreet to give me the power of MS Exchange. It works beautifully. The only caveat with Mac is (at least the version of Entourage and OS I have now) that the sent mail from Entourage won't be able to be pulled up on your BB. Also Tasks and Notes do not sync to Entourage but Calendar and Contacts work great.
I know there are others, in fact I just saw an ad from Link2exchange and its offer for 6 free months.
I am very happy with Mailstreet though and have been with them for over a year now.
The other benefit is your mail is now stored on their servers and you don't have to worry about hard drive crashes or losing your BB. The power of Exchange is great, I would Google "exchange blackberry" and read about it.
Good luck and let me know if you have any other questions.