We've been doing the 2-liter bottles of ice for our buns, and they love it. We don't put them out there until it is at least over 85*, because they need to last into the evening, when it finally goes back below the high 80s.
They go nuts over them. Some of them dig at it, lick it, play with it. Others just lie down next to it. Thumper lies down with his forehead against it, after he licks it to death first like a giant popsicle.
Once, Ilovebunnies found Thumper breathing fast, and he was somewhat listless, rather than looking for attention (we had forgotten to put the ice bottles out for them). She remembered something she had read in a book, and got him out, sat him in her lap, and held ice cubes to the insides of his ears. Since the ears are the way the rabbit gets rid of excess heat, ice held to the ears is a very direct way to cool the blood and therefore the body. He just sat there and took it, though I can't say it would be that easy with every rabbit. Shortly afterward, he was back to himself again.
I told Ilovebunnies she probably saved Thumper's life, and that I was really proud of her.
I have heard of freezing tiles before, and I bet the buns love that too! I don't know how quickly they warm up compared to the ice bottles.