I wanted to post my initial thoughts and results for using the Igloo 70 Quart Ice Cube MaxCold cooler (linked below).
With the lid off, it has been holding perfect temps (~63) for not only the water but also the 6.5 gallon carboy beer temp. In fact, it worked so well at first, the initial water temp was down in the lower 40's until I warmed it up. Great cooler if you don't want to invest in a freezer or refridgerator yet. I haven't even bothered using the lid that came with it or a makeshift styrofoam lid.
-Keep in mind if you go this route, the standard lid won't close with a 6.5 glass carboy.
-The above results have been in Florida, ambient temps in the low to mid 70's inside. http://www.walmart.com/ip/Igloo-70-Quart-Ice-Cube-MaxCold-Roller/16606386