A pc tower case is the unit you use to hold all the accessories in your computer together, including the power supply, the motherboard and all the internal drives. They come in all shapes and sizes but are usually made of metallic components of some description. There are so many different products to chose from its not even remotely straight forward to just go and chose one, so I though I might give some ideas on how to get the perfect case for your stuff.

Sizes

It’s not just the external size you have to look for when deciding between candidates, the size of motherboard it can accommodate is also of interest. Most common desktop motherboard standard is ATX, but there are a few variatious you may run across. Micro ATX, or mATX is one of the more popular solutions that is just as wide as a normal one, but cropped in length. A standard pc tower can take both variations, smaller form factors are upwards compatible, so to speak. Once you’ve decided which type your main board is, you can go on to other parts to see if they fit. Modern cases come with 3-5 bays for 5,25” drives such as DVD or blue-ray units, and a few slots for hard drives. Check the product in subject for number of these bays before purchase, because there is few more frustrating things to bear with than one less slot than the number of your hard drives. That said, 90% of the time you will be fine, just take a careful look around before giving a few dozen bucks out.
Color and shape is entirely up to your liking, but build quality should be of concern, so if you think you have found the perfect size, shape, form factor, color pc tower case check the quality of manufacture before purchase.

Things to look for:
-Sharp edges around the inside circumference. Noone wants to bleed after assembly
-Sharp edges near the bottom, where PCI cards fit
-Bending of elements. Pc towers shouldn’t woggle as soon as a fan starts blowing inside
-Scratches, issues with painting. If you have the opportunity and time, check for these too
-Dents. This with the above are almost always issues with shipping, but you shouldn’t settle for less than what the manufacturer intended to produce.

Prices

It is normal for a pc case without included power supply to cost from 30 bucks to 300, depending on size, quality and materials used. A case made of 1/26 inch thick stainless steel most probably costs 3 times as much as 1/48 inch thick aluminum composites. Weight can give you a rough estimation on quality of components used.
Some manufacturers to check before making the final decision (without importance of order):
Lian Li, Casetek, Chieftec, Antec, Aopen and Cooler Master. These are makers who emphasize quality so be prepared to pay up to 2-300 dollars for a more exclusive tower. If you are looking for cases good enough without the horror price tag, take a look at what Codegen has.