Well, (s)he was still limping yesterday. Not out scratching with the others. Just lying down in the weak sunshine. I'm new to chickens, so I checked the sort of things I'd look at for any injured pet or livestock animal.
Eating/drinking? Yes to both, just prefers to do so from a prone position.
Eyes are bright and clear.
Bird is alert.
Skin/coat- Wattles and comb are normal colors (just assuming that sick bird might have pale comb), no obvious abrasions/bruising/swelling anywhere, feathers have a healthy sheen.
The only off signs are the limping, lying down most of the time, and calmness (this bird is normally very skittish). I went out and caught him last night, and he only half heartedly made an escape attempt. All I got was an outraged squawk. Didn't even peck me. I held him until he was totally relaxed, and checked both legs and feet, though he appears to be favoring the left. Bones seem sound, no abrasions or discolorations. He didn't seem to mind the poking and prodding. He actually seemed to be enjoying the attention. If he is a roo, and he recovers, he may end up a friendly bird. Maybe.
In any case, not sure what else to look for. Any suggestions would be welcome. I'm hoping it's just a sprain or something of that sort. He is going in the coop each night and coming out during the day. If it gets worse, I may bring him in and put him in a crate for a couple days and see if that helps. Ah well. We'll see how it goes.
(update, July 2011... This bird recovered completely, and we never figured out what was wrong with him. Yes, him. He is a monstrously huge and lovely Welsummer rooster.)