I agree with aircooled, any old modem will work just fine, as long as your not a gamer. If you are then I would recommend the Diamond Supra Express External Serial modems, the single greatest modem in the history of the universe. You can find them used on ebay for 30-40 bucks. Here's the ping to the isp...
Host Name IP Address Hop Ping Time Ping Avg % Loss Pkts r/s Ping best/worst
arc-6a.hou.mindspring.net 207.69.219.88 1 69ms 74ms 0% 275 / 275 68ms / 83ms