Many of the EC trains in southern Germany are run with DB rolling stock, and are indistinguishable from the German IC trains.

The ICE features a 220V outlet for every 2 seats, and (in some models) a 6-channel audio program (of questionable quality). The IC features 4 220V outlets per car, and not even a chance of audio. Many ICEs still (or again) feature a full dining car; most ICs don't.

Another difference is the speed...but that depends on the route. For example, I travel frequently between Stuttgart and Munich. The price difference is 6 Euros, and the time difference is...usually about 1 or 2 minutes! That's because this is not a high-speed line. On the other hand, if you travel from Stuttgart to Cologne, the difference is 30 Euros...and 90 minutes!