During the summer time I pre-chill my cooling water by filling my (rinsed out) mash tun with ice water and pumping that water through the immersion chiller. In the past I would save milk jugs and make big blocks of ice with them. However the ice is never easy to get out even if you cut the tops of the jugs off; I usually wind up smashing them with a ball peen hammer.
Well it turns out ice cream buckets are the way to go. They have a smooth plastic interior and are conically-shaped so that your ice will slide right out. Reusable too!