Kiva set the concept of P2P finance in motion, without doubt.  

C4 world is another I've come across in my virtual travels, an org from Europe: 

http://www.myc4.com/Portal/Default.aspx

Then there's Zopa 

http://uk.zopa.com/ZopaWeb/ 

Even more interesting to me is the concept of asset based finance rather than debt based microcredit. It comes from a former City of London regulator whose ideas came long before the sub-prime crisis.

http://www.opencapital.net/

Under the Guarantee Society model of asset based finance, credit is advanced in "time to pay" with default being protected against by a communal fund.