M.D.
Our morning sitter is from sittercity.com. She is FABULOUS. My sister's both have been on sittercity.com too.
Just want to point out that doing all of the research you can on someone won't guarantee a good person. We hired a full-time nanny from sittercity.com in September. She came with GREAT references, her background check was clean, and she was no where in the MD legal system. BUT...when she was frustrated with my 4 year old, she pushed him. I let sittercity.com know and they called me and took her off of the site! YAY!!