Ask Slashdot: SIM-Card Solutions In North America?

An anonymous reader writes I'll be returning to North America for July for the first time in a few years, and I'm curious how the phone carrier market compares with the rest of the world. My last time in the U.S., I had to pick up a disposable phone with all kinds of unnecessary environmental waste (charger, packaging, etc.), and *still* had to register it with another domestic (!) phone number and credit card. I don't think I could get a SIM card there without a contract. Anywhere else I travel, picking up a new SIM card with pre-loaded credit is trivially easy. In my last trip to the UK, I just put GBP 10 into a vending machine at the airport and picked up a loaded SIM card for my phone which aldready has my contacts and settings. No ID, no name, no hassle. What are the best options for me in North America (U.S. *and* Canada)?