You can enable push with gmail. I use it all the time. You set-up a Microsoft Exchange account.
Here's the step-by-step from Google:
http://www.google.com/support/mobile/bin/answer.py?answer=138740&topic=14252
With this set-up, you get wireless sync of your e-mail, contacts, and calendar. I've got it set-up on my iPhone 4 and iPad and it works great!
And the best part is that it's free.