The best thing to use is a soft, non-abrasive cloth lightly dampened with water. Also, be careful around and cracks/openings/seals, especially the display, since it's not a tight seal...water or any other liquid can run in. You can use a light cleanser on the body if necessary, but I'd still be wary of using such on the display.
Hope this helps,
This is a really simple question. I've held off getting a Blackberry as long as possible, but I've gone ahead and taken the plunge and gotten a 7290. My question is the screen/monitor has smudges on it. What can I use to clean it, or how should I clean it?