I agree with Bar-Code. For the DIY approach teragen is the best option out there. I used it many times before getting Bryce. Both peices of software will do better then what any Photoshop plug-in I've looked at.

Also if you have P6 the skydome is a great option.

If you've still haven't gotten anything when I get home (say like in 5 hrs) I'll whip you something up in Bryce real quick.