I have to disagree with ejsmith. If you skimp on your case and/or power supply, you will regret it for a long time to come. I am replacing the case on my little "Ol' Faithful", and I am looking forward to spending $100 - $150 for a case/PSU combo. Think about what you want in a case and then go from there. Things to think about: steel or aluminum, detachable drive bays, slide out mobo tray, ventilation/fans, etc...
As for specific suggestions for cases, I keep hearing about Antec and Chieftec, who make cases that are identical to some of the Alienware systems. Also, Kingwin has some sleek looking windowed cases that are geared toward gaming systems...
As for PSUs, Antec and Enermax seem to have a pretty good following in the community here, due to their highly clean and efficient supply technology and power-saving and acoustic-dampening features. Noise is a big problem for me, so I will be looking to get an Antec TruePower with built-in noise reduction features...
Anyway, when you decide what your priorities are, then you'll have a better idea of where to look.
Happy hunting!
-DOOM