If it has to be a blackberry, then the newest one is the new curve. I'm not too familiar with blackberrys, but there is one non-blackberry (but still a smartphone) that seems very nice.
It's called the HTC Touch Pro 2. It's a touchscreen, and it has one of the best slide out keyboards. It's one that I'm looking into getting for myself, it gets great reviews and ratings, and there are some great software tours to check out on youtube if you want to know more.
Hope I helped!
