My all time favorite is Graeter's Chocolate Chocolate Chip. Say what you will, but it's heaven to me.
After that a toss up between Ben & Jerry's Americone Dream and Phish Food.
__________________ "If you want to criticize my methods, fine. But you can keep your snide remarks to yourself. And while you're at it, don't criticize my methods." Rupert Giles, BtVS