Phone randomly black screens, forced to remove battery and reboot
I think I had the same problem recently. When I pressed the phone's power button to wake it up, the display would turn on, but stay completely blank. It happened multiple times a day for me and I got frustrated, so I tried three things and one of those seems to have fixed the problem. Knock on wood.


I reformatted my external SD-Card.
I removed almost all of my media files from the phone.
I disabled JuiceDefender's CPU frequency scaling


My prime suspect was the SD-Card, because the problems started to occur, when I inserted it, but I cannot be sure.