You can use just a regular one. But most guys, and myself, have switched to a compression short style cup design by shock doctor.
http://www.shockdoctor.com/coreProte...mpression.html
Like the ones on this link. They work very well and are very comfortable. If you are just starting out in MMA, grappling, or kickboxing? I dont know which. Its better that you go and just wear some gym clothes and train a little bit and see if you really like it or not first. That way you dont end up spending lots of money on gear then deciding, well I dont really like this. So hold off on the sprawls and gold weave gi just yet. If ya like MMA, then the guys on this forum can help you out so much with the best gear that they have used and abused! Hope this helps ya, ask more questions if ya got em!