Surprisingly, he was very affectionate and cuddly. He had a collar around his neck, but no tags. My sister didn't want to take him to the pound like we originally planned, because they'd just put him down. He slept in the basement overnight, and was put out the next morning.
I thought that would have been the end of it, but every day since then he's been showing up near our front door and meowing for attention. He'd run off and hide once someone came out, just to creep back into view and walk close once again when he saw who came out. The next day we ended up bringing him into the basement to sleep overnight again. I spent some time that night with him, cuddling him and petting him and all sorts of cute affection you give to a small animal. Now, there's small, and then there's this cat. While not a kitten (we think he's 2-3 years old) he's bone-thin. You can feel the ridges in his spine as you run your hand along his back, and his stomach is sunken in a bit due to not eating well. So we fed him, and let him out again the next morning.
Well, he just keeps coming back. The next two nights we tried to ignore him but at least once a day, he would show up and meow. Yesterday he caught a glimpse of me at my bedroom window and meowed at me for several minutes before my heart melted and I came outside with a small cup of dog food. Today he came by again, around the same time, and was watching for me at the windows by the front door. I came out with some cat food this time and poured him a small pile to eat right on the front steps. He enjoyed it; his purring is almost as loud as the meowing, at least.
As winter approaches, it's been getting colder and colder out. Tonight I stepped outside, sat on the front steps, and made little smooching noises with my lips to call for him. 15-20 seconds later, he slinks out from the bushes and comes over to me to be pet. I pick him up and take him inside again.
Right now we have him in the basement. He has a little towel for a blanket and a litter box for him, and we're going to get a vet appointment for him soon. He'll probably be staying for at least the winter, unless we somehow come across his owners. Without any tags, though, it seems rather improbable that we'll find them.
I don't have a picture of him so I just snagged a picture of an orange tabby off of a Google image search. It doesn't look -quite- like him but it's just similar enough to put a picture in your head. No white underside though.

Unlike the cat in this picture, the one we took in has very sharp, piercing eyes. It's like he's always studying you.
Holy freaking crap man, GET THAT CAT OUT OF THERE! Its either a Man/Woman trapped in a Cat's Body or an Alien.
RUN, MAN, RUN!
(To end on a lighter note, the picture is quite cute.)