Get DSL and hope that you live fairly close to the phone switch. That is the only practical way to get a low ping.
Second is to get a business T1 line and the list goes up from there.
I know too many of my friends that have cable modems and they will get varying ping times throughout the day. Keep in mind that ping varies because of use of the cable line and the signal strength at your househood. One cable contains many signals to multiple househoods. Anyone changing channels is going to affect ping. Just think when 10 or 100 TVs changing channels at the same time and that doesn't include other users surfing the 'net on their cable modem.
Remember this key point...
better bandwidth does NOT equal better ping times
Anything with a dedicated line is much better for pings, i.e. iDSL, aDSL, T1, T3.
The best pings I ever had was with iDSL (most DSL lines today are aDSL) that had a 144kbps max. These pings were always lower then what I am currently getting with my aDSL line.