AnandTech published a case and power supply buyers guide, you can check it out over here. They picked the best products for each price class.
Computer Component suppliers normally sell the case and power supply as a combined purchase. The prices often seem to be a good value, but our experience has been that it is often tough to determine the source and quality of the Power Supply used in the package. Combo cases are often the cheapest and thinnest metal you can possibly buy. These combo Case/PS may be great for a retailer building entry systems for resale, but they are rarely high enough in performance or durability to meet the needs of the Computer Enthusiast. They also may work fine initially, but the cheap kit power supplies are often the first things to go in a system.
For all these reasons we recommend the separate selection of a case and power supply for a new system build, or to replace the case you now have. The price and performance range among current cases and power supplies is huge, so we have zeroed in on some typical price points for knowledgeable shoppers looking for a new case or power supply.