Do you want a mid-tower or full tower? ATX is the way to go as most mobo's and other parts use the ATX standard size.
Antec is a good company, so is Cooler Master.
My 2 prefered Mid-Tower cases right now are below.
Cooler Master Storm Scout: $79
http://www.newegg.com/Product/Produc...82E16811119196
Antec 902: $109
http://www.newegg.com/Product/Produc...82E16811129097
For Buying online, Newegg is probably your safest bet with the best Customer Service and decent pricing. If you have a Fry's Electronics locally you can sometimes find better deals on cases in their Brick and Mortar shops. But not always.