If you use Gmail at all, you really need to check this out. It’s a Java-based client for Gmail and it really kicks much ass. Google even included some neat functionality. It pre-caches messages so that when you get to them they open almost instantaneously.
I installed it on my BlackBerry Pearl and it was so good I’m using it as my primary method of connecting to Gmail. As is usually the case with Google, this is well thought out and includes just about any function you would want in a mobile client. Go check it out. You can download it directly to your device, if it’s supported, by going to http://www.gmail.com/app.