Nota Bene: All of the organizations listed below are specific to San Antonio, Texas. As eSamaritan grows I hope to add organizations like this all over the country. Right now I will start with the ones that I know of and have worked with.
Haven for Hope truly is a one of a kind. Their goal is to help homeless get back on their feet by offering them a wide range of services for no cost. They work with about 80 different organizations that are all onsite and is the largest campus of it's kind in the entire USA.
SAMMinistires is a shelter for Homeless families. They were founded in 1983 and have been doing this for a long time. I have been there before to help feed some of the families and it is a very rewarding volunteer experience.
Christian Hope Resource Center does homeless prevention for San Antonio. They are directly helping hundreds of families that are on the verge of being homeless but are not. They operate a food bank that feeds about 400 families a week. They have a onsite clothing store where people can have 5 articles of clothing for free. They are also the organization of choice for doing community service for the city. Great partners that are doing amazing work in SA.