If you don't mind paying for Mobile Me you get push email and wireless sync of your contacts, etc. I have MoMe because we own Macs so for me the wireless features were "free". It's not a terribly good deal as there are free solutions out there that have already been mentioned but I just want to make sure every knows MoMe offers push email. BTW, BB email is different than exchange. You to to RIM's server and it "pulls" your email from whatever POP or IMAP account you point it to and it pushes it to your phone using something very similar to SMS. It also uses data compression. I doubt RIM licensed exchange technology from MS for their push email. It's something they set up for themselves and it works with any email account you own.
BTW, how do I know RIM's server is "pulling" my email? I got locked out of my gmail account when I had RIM's server pointed to it and had a bad password setup on RIM's server. I had to spend hours "unlocking" my gmail account and filling out image captcha's for each and every login attempt until I realized what was going on, shut off RIM's server, waited 24 hours for the "hacked flag" to expire and was able to log in to gmail again. Now gmail offers more options including text messages to unlock accounts but this was before all these nice features were added. So it's not accurate to say RIM is using exchange. It's something similar to exchange but definitely proprietary to RIM and BB devices.