I'm fond of freezing water (or tea) in rectangular Nalgene water bottles -- especially this 64 oz one below.

http://www.rei.com/product/402058/nalgene-space-saver-bottle-64-fl-oz


Nalgene makes several smaller rectangular bottles, including a 32 oz. I've got several in the freezer right now to throw in the cooler for a weekend trip.

One of the aspects of using water bottles for ice is that we can drink the water (or "iced" tea) when it melts.