Code Answer: Find out what sites are powered by

Any online tool/service that tells you what sites are powered by?

From stackoverflow

For javascript frameworks: http://blog.olicio.us/2008/11/08/wtframework-bookmarklet/ In Web frameworks, sometimes you have the : X-poweredBy header...

an ecommerce or multimedia platforms, no idea
builtwith.com gives some good info on sites..

Jenko : Ha ha! Just re-found it myself but you beat me to it!
eCommerce enterprise probably isn't too extroverted about broadcasting on sites that their technology is being used, since it opens an additional security vector. I have no way to verify that, it's just a guess.

That said, looking around in the source code helps if you know what to look for. You can also ask the proprietor/tech contact for the site.
I thought I'd never find it again but anyways...

BuiltWith - Web technology trends. Find out what a site is using.

Topics profiled in websites: (click to view worldwide trends)
I have developed http://poweredsites.org for this issue, you can find a list of python powered sites from python.poweredsites.org, django powered sites from django.poweredsites.org, jquery powered sites from jquery.poweredsites.org etc.

Have fun.

Code Answer