My cable modem is an RCA supplied by the cable company, but I don't pay a monthly fee on it.
I signed up when they had a deal for free set up, free modem and one month free. Considering what I pay though, it's the least they could do.
I might try a new one to see if it is any faster, but I can't complain much about my download speed. anywhere from 10-15mb/s.