Is there a place on MSE where one can post interesting non-interrogative math stuff? Like for instance this amazing thing that I'm sure everyone on this site would benefit from (and of which I suspect everyone is already aware): http://webdemo.visionobjects.com/equation.html
That site may fall under "useful tools or resources for the mathematically inclined" and hence could be a good candidate for community ads.
But other than specifically mathematical links that fits the community ad scheme, for generally sharing of awesome stuff I refer you to Google+, Twitter, Reddit, or your own personal blog for that.
You could post it as an answer to Resources for getting maths on to the web. It might fit as an answer to https://mathoverflow.net/questions/2147/most-helpful-math-resources-on-the-web