ATX or Full ATX case?

Building a computer and I'm having trouble choosing a case, the graphics card is a tank (ATI Radeon 6850) so I need to make sure the case is big enough to store the card. Is there a difference between ATX and "full" ATX? Additionally, if anyone has this card it would help if they could let me know which case they're using, looking for something fairly cheap (~�50) with good airflow.