This topic of receiving Push notifications for your Gmail has been discussed more than a few times, and there are more than a few options available. Personally, I use the Prowl/Growl combo, however others have reported good experience with PushMail as well as NuevaSync.
Additionally, there is the simple GPush app which gives you a Push alert when a mail message is received, but there is also another app that I just found. Of course, it looks like it has been out for a little while as the release date in the App Store is showing June 30, 2009.
Anyway, the app is called G-Push Mail, and is priced at $1.99. Similar to the other Push-related Gmail apps, this one promises to offer “true Push Gmail for your iPhone.”
This app does come with a drawback, at least as far as I am concerned — it requires a monthly subscription to be used. Users will have to pay $1.99 for three months of use, of course, my feeling that is a drawback could just be due to my lack of importance in regards to email. I like the Push alerts, but could deal without them, my main reason for using the Prowl/Growl notification is more in terms of saving my battery by having my mail setting to Manual in terms of checking for new mail.
Otherwise, the G-Push Mail app is not a forwarding service like PushMail, instead it actively maintains a connection with Gmail’s IMAP servers using Amazon’s Cloud service, which is a good reason for a monthly fee.
Other features that make G-Push seem like a nice alternative is the ability to monitor all of your mail or just your inbox as well as the ability to change alert sounds. Additionally, it also ties in with Gmail’s web interface which gives you easy access to your contacts, as well as the ability to search your mail from your phone.
All things considered, theG-Push Mail app seems to be a viable option when it comes to receiving Push Gmail alerts. I will say that I have not used this personally, but if you want, there is a nice review over on iPhoneInCanada.ca.