In addition to Kryptonite and OnGuard, Abus makes good U-locks. I have the Granite X-plus something or the other, and it spends a lot of time out in the elements, including wintery conditions. I oil it lightly VERY occasionally. It has never jammed.

You would get more lock options by moving over to hardened steel chain + padlock combo. But that combination can be heavy and expensive, especially if you aim to maximize security.

--J