Weddingbee boards

I came home from work for lunch and was walking my dog.  A stray yellow lab came up to us and followed me home.  I have a 9 lb toy poodle, so I picked him up and brought him inside because he usually get scared of bigger dogs.  The lab jumped on me a little to try to sniff my dog, but seemed friendly.  He didn't try to bite or anything.  Well it's raining and after following me home, the dog has stayed on my porch.  He was crying and howling and all skin and bones, so I went out and gave him some food and water, which basically just guaranteed that he's not moving off my porch, but I had to do something!  I called animal control, but they said that he would be put in a kill shelter and if someone didn't adopt him within 30 days, he would be put to sleep! So I told them not to come because although he's sweet, he's also older (lots of white in his face), so I just don't think his chances would be good to be adopted.  That's also my problem with bringing him to the humane society.

I don't know what to do!  I have to go back to work, and I absolutely do not feel comfortable leaving a stray dog inside my house with my little dog, so that's not an option.  I'm going to put a post on craigslist, but people around where I live don't really use craigslist, so I doubt that would be helpful.  WHAT SHOULD I DO?  I want to take him to the vet to get all his shots, then I would consider introducing him to my dog.  I have a spare bedroom that I could keep him in, but I don't want to put my dog in any danger.  Any advice?

ETA: The dog doesn't have a collar or tags.

Thanks for the responses!  Unfortunately, I don't have an enclosed laundry room, porch, garage, etc. for him. I just have the spare bedroom or bathroom, but like I said, I wouldn't really feel comfortable putting him somewhere my dog normally has access until I get him checked out. My porch is covered, which is probably why he's hanging out there.  I left him more food and water before I left to come back to work.

I ran into my neighbor, who is retired, and he said he would keep an eye on him until I get back from work.  I'm going to bring him to the vet and see if he has a microchip.  If he doesn't, then I'll probably get him a checkup and assess my options.  As much as I would love another dog, I don't think I could have a lab.  My toy poodle really doesn't like bigger dogs, and I need to look out for him first.  I'm going to call around and see if I can find a no-kill shelter or lab rescue as some of you suggested. 

@nickels: No, I'm in Panama City, FL.  I'm from Boston though, which is where I got my username. 

Update!  When I got home from work last night, my neighbor (who was keeping an eye on the dog) said that his owner was out looking for him and found him on my porch.  The owner said she leaves him in her fenced in yard during the day while she's at work, and he got out somehow.  She lives 3 blocks away. I'm so glad he got to go home!