Denny's

The food is generally plentiful, and the prices are not unreasonable given the size of the portions; on the other hand, one may not _actually_ want three pancakes, two sausages, some strips of bacon, and an omelette at 3am (which is, for me, the time of peak interest).

The service can be on the slow side when they're at peak capacity, but generally the staff at this location are polite and friendly.

Well... it's a diner. There are plastic-covered booths which are basically kept clean, but it's not going to impress you in terms of environment.

If you're after something a little more upscale late at night, check out Wokcano (link to the side).