SPCA and local animal rescues are the best places to look. You can also check out Petfinder (which will have cats from rescues) and Craigslist. I personally have had great success in Petfinder and in the SPCA. Pet finder gives you the time to read through all of their descriptions and meet up with the animal as many times as you need.
There are multiple reasons I am not a fan of the humane society, and mainly because they are not at all humane. This is all of them and they get absolutely no funding to really take care of their animals. They've lied multiple times on the paperwork when I have been with people that rescue cats there. They don't tell you any of the health problems and then later people are slammed with vet bills. They also don't give their animals much time to live there and will euthanize them within a few days of arriving. The SPCA waits years to even consider euthanizing and even then the animal has to have problems or be sick. They also make sure to take good care of their animals and find foster homes if they run out of space. Most local pet shelters are no-kill and they put a lot of effort into taking care of their animals because many are in foster homes.