Yesterday I got my Antec 300 and I am delighted with it. With that, it means I can modify my old case (a Xion Onyx, if anyone is interested), and one thing I wanted to do is flip the top-mounted PSU over and have it exhaust its heat directly out of the case. I'm a confused though: I've searched...
I just got myself an Antec 300. Awesome case, fits my 4870 nicely (with space for one more), looks awesome and the cooling is fantastic (I stuck 3 Akasa Silent Blue 120mm fans into it, keeps everything very cool). Its about $60 on Newegg, but I'm sure it can be had for cheaper elsewhere...
3 x 5.35inch drive bay covers, a bit of super strength glue, 1 x 120mm fan plus fanguard and 15 minutes with a dremel = ghetto fan mod.
And pictured below is the old 550watt PSU I ripped the 120mm fan guard from.
Needed to exhaust some of the hot air from my HD4870 card, so I slapped a 92mm fan in there. Works well, dropped ambient temps by about 7°C and dropped my GFX idle temps by 15°C. Under load it can still peak at about 80°C, but at least it isn't pushing 100°C anymore.