Im using NTL Cable on my Amiga via A Belkin 4-Port router (about £50), although i used the pc to initially setup the modem before plugging router in.
Initial problem was getting the Amiga to stay online, ,as it was using dhcp to get an ip from the router. Solution was to make the IP static (same ip that router issued via dhcp)
Since i use Amiga mostly for irc I chose to make the Amiga IP the one to enter in the DMZ (Since only one ip can be entered on this router) This disables the router wall for that IP. (was required to make DCC work)
So i use Miami IP Filters to enable/isable ports i wish to use (also this router doesnt seem toallow port ranges so can only open individual ports via a trigger port).
this method is working ok for me