I am currently using my 8300 bb case, it fits nicely and puts it in sleep. I tried others and the fit was either too tight, or the magnet was not closing right, therefore not putting it in sleep mode.
Posted from my CrackBerry at wapforums.crackberry.com
AT&T has a leather case for the curve for $5. I tried the one I had for my curve and it fits good and it puts it to sleep. I'm ordering 2 at that price.