I use a 1/6HP utility pump I found used on Craigslist for $10.
You definitely don't want to cycle the icewater until you've hit a your temperature has stalled with tap water. For me (Northern California) I chill with tap water through my IC until I reach 80F. This takes about 10-15 minutes. Then I switch over to the utility pump in a cooler with ice. One bag of ice will take me from 85f to 68F in another 10-15 minutes. So for total cooling time, half of which I'm not wasting any water I can get right to pitch pitch temp for ales. For lagers, I add another bag of ice at 68F and can get down to 50F or lower in another 15 minutes. It's a great set up.
One thing that really helps the cooling is to rig a whirlpool around the IC. It's amazing how much the increased surface area will cut chill time.