Hi C.,
I do dog fostering/rescue in Longmont. I can't say enough good things about Longmont Humane. :)
I think you should consider first, what type of dog you are interested in. Big, little, mutt (my personal fav. besides Beagles) etc. There are so many breed specific rescues in our area. I know the folks at the Beagle rescue. Additionally, some breeds require more exercise than others (Bully breeds, Jack Russel Terriers, etc.)
Check out petfinder.com too. It's a GREAT resource.
If you are busy, work full time, etc. I would recommend older dogs. Puppies get adopted so fast, and honestly, they are a pain in the butt to housetrain. They eat everything (pillows, toys, stuffed animals, etc.) My beagle whom I got as a pup ate numerous dog beds, pillows, shoes (my favorites too) and just need so much exercise to stay out of trouble(1-2 hours a day). If you aren't that active consider an older dog.
Good luck!