If you're doing CAD and trying to play games, I would NEVER recommend a Celeron processor. I also would say don't get a 15" display. I've owned a 17" laptop and it was bulky and awkward to use on anything except a desk - not mobile at all.
I browsed Newegg for a little while, which is 1 of 2 sites you should consider for PCs and PC parts, the other being TigerDirect, and came across
this which seems to fit your budget and should be decent. I'm not a fan of the i5 over an i7, but the display is better than some 17" laptops I've seen at 1920x1080, and the RAM should be fine for gaming and CAD. To be honest, you'd be most likely to bottleneck on HDD speed, so you could consider updating to a 7200 RPM drive.
I've been a fan of ASUS laptops for a while now, so that's what the link is, but also consider the Dell Studio line.
Hope that helps.