Markdown Live Preview Editor?

I am currently using Textmate to create Markdown documents, but it requires me to press CtrlOptionCmd + P everytime I want to 'update' the Markdown output window. Essentially I am using it like a word processor. Is there a Markdown editor for Mac OS X which supports wysiwig/live update of the content? Perhaps Textmate already does this?

[mattn]

そういえばこれ関連でVimって無いよなー。