Here are a few starting points:
RIM Phone Index - RIM wallpapers, ringtones, themes, videos, games downloads
Blackberry Wallpapers
Mobile Software & Games for your PDA or Smartphone : Handango
I've used one at school in the lab, dont have much flight time on it yet. I have noticed one thing with it, when receiving e-mail and if your on a separate phone, you will hear pulses of the data stream on the phone, kinda a EMP cross talk thing. I'm glad school is paying for it in the lab, I couldnt afford the device/service myself.
Enjoy.