I'd recommend an Inwin case, one of the old classic black ones would look nice (the new ones look kind of cheap). They come with good power supplies.
If you're looking for something flashier, a Chieftec case would be great, and Fortron makes the best power supplies
All these are available at Newegg.
Full sized ATX cases use full sized power supplies, which are the same size as the old AT power supplies. Smaller cases can use either standard ATX (aka PS-II size), PS-III, or SFX. So unless you're buying a small case, you don't have much to worry about.
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