Funny you should ask, and welcome to the forum....I just read an online article, cant remember what linked me to it, but the most popular microfinance org within the US, is called Accion USA.
http://www.accionusa.org/site/c.lvKVL9MUIsG/b.1359227/k.F8F8/Small_Business_Loans__Microlending__Business_Loan.htmUp until 2005 they only worked in select cities, but now serve most of the United States.
As for Kiva offering loans to Americans Im not sure that will materialize because the standard of living is so very high. Even if only 100 people needed loans of $10k each for business purposes, thats still one million dollars, just for 100 people, while Kiva in working around the rest of the world, has funded over 17000 loans with just over 11 million dollars as Im sure you know, so you can see the difference in numbers. Funds go so much further in developing countries.
There is a Kiva similar site called Prosper.com, where people loan to one another.
Great to have you and please do speak your mind. This is an incredible forum.