Google's just announced a new version of mobile gmail. According to the press release it's US/Canada only, but I've just downloaded it in London and it works a treat!
It's a Java applet that works on any J2ME enabled phone and provides the cool GMail stuff like conversations view, searching, stars, and attachments
It looks really slick, very much a GMail feel and it's lightning quick. I was a big fan of the old-style mobile GMail and this is a big improvement over that. Check it out on your mobile by pointing it to gmail.com/app.