The previous person gave some great options. The only other one I can think of is to find someone with an office and to get permission to use their address for your business. You may find that if you know the person they may have no problem with it since you are not actually using space there.

Good Luck. Fortunately for me that's not a problem. I'm in an apartment too but we can use apartment addresses for home businesses here. That's one pro to living in Utah, nearly everyone has a home business.