I downloaded Gmail’s mobile app onto my Black Berry 8330, and I like it. The app gives you quick access to your gmail account on your phone, and works a lot better than simply going to gmail.com on your phone’s browser (which I was doing before). The application is free (of course, your carrier’s data rates apply), and you can download it to your phone by pointing your phone’s browser to: http://gmail.com/app
I would say the only thing that might be a problem for some is that once you enter your e-mail address and password it seems to save it in the app. This is convenient, as you can quickly access your inbox by simply opening the app, but the security conscious may not like this. There is a sign out button, but you have to choose it specifically in the menu before exiting the app. You can have more than one gmail account added in the phone and switch between them, but I haven’t played with this feature as I only have the one account.
Anyway, if you have a Black Berry or similarly modern phone and a gmail account. Give it a try.