The Motorola SB4200 is a great modem, SB4100 is alright, andnow we are starting to see the hSB4220 and they seem to be just as good (although I have had one doa for the SB4220which has never happened to me with teh SB4200). I don't really like the 3COM and the RCA often seem to have problems. We don't see many Dlink or Linksys but they seem to work alright. Toshiba's rank right up there with the RCA in the suck category. Com21 are good but ugly. Just my opinions.
[EDIT] BTW I'm probably going to get a Linksys modem soon since I have a Linksys router and the stacking option is great. If I didn't have the router I would deffinetly go with one of the Motorola models, especially since in my area Circuit City is giving them away with activation.