try freezing half a bottle full of water the night before. then fill it up to the top when you go out for your ride. on hot days, i just freeze the whole bottle, and use an unfrozen bottle for the first half of the ride, and switch to the full frozen one after it's started melting.
there is also this:
http://www.qbike.com/cgi-bin/bike.cg...bottle&auct=on
And also some of the dark aluminum bottles are good at preventing radiative, but not convective heating.