[PonkiPoodles]

Most people foster for they're local animal shelter or rescue. You can usually just contact them and tell them you are interested in becoming a foster.
You can find local rescues and animal shelters by search for them on petfinder.com - just use your state and city to search:
http://www.petfinder.com/awo/index.cgi?action=state

After you sign up as one of their fosters, most rescues do give you information or help you as far as getting the dog you are fostering adopted out.
I've been a foster for many years... and I have pictures of every single dog I've fostered. Some take longer to find homes than others and some end up staying for good (as you reach a bond that is truely unbreakable)
It can be pretty challenging at times, especially if you get puppy mill, abused, neglected dogs.... but seeing how they eventually turn out makes everything worth your while.
Hope this answers some of your questions

 

[PonkiPoodles]

Before you take them home do you make sure they get along with your other dogs or do you gently socialize them? I am definetly going to wait until me and penny have done some work with our relationship with the move and all and training classes! But I just don't want my penny to feel bad if there is a new addition! She does well with other puppies we've met but there's always that thought in my mind? I'm thinking about volunteering in the shelter until I can foster and feel comfortable to take an animal home with me.

That’s a great question. I’ve taken home many aggressive dogs... either aggressive toward other animals or fear aggressive.
Since you are new at this, I would recommend you take home a dog that the rescue or shelter already knows gets along with other pets or if your shelter get's puppies that would be your best bet.
With fearful or aggressive dogs I usually crate them for a couple of days. Meaning they have no access to my house other than when I take them out for a walk or potty break . This helps them realize that you are the pack leader and they are going to live under your rules. And it makes your life a whole lot easier.
I also do not introduce them to my pets right off the bat. I crate them because this gives them a change to observe a new surrounding without feeling threatened, to get use to the smell of my home and pets and just to relax a bit and get use to the change.
When I eventually introduce them to my other pets, I keep the foster crated and let him/her meet my pets one at a time. If it goes well, I let the foster out and have them socialize with one pet at a time. This is just so they don’t get the feeling of a pack attacking them - because your pets already consider themselves a pack, letting them all meet at once might make the new foster even more fearful.
Eventually they meet another family member and another... and are slowly integrated into my household. I’ve tried this method with many different dogs, and I’ve taken in dogs which the shelter said will never be able to live with other pets - funny how most of them eventually were adopted out to homes with other pets?!?!