probably tableau public gallery? I think you should be able to publish it from within the tool.

Infographics & data visualization gallery | Tableau Public

Great question.  If you are wanting to share with the Forum, a Workbook & Calculation Library exists as well although I'm not sure how much traffic this area receives.

Jeffrey Strauss wrote:

 

If I have a really cool viz, where is the best place to post it?  I'm really confused with all the different forums available.

My man, you're not the only one!