module usage

I'm new to Drupal and found several sites where I like the layout and functionality. I'm trying to figure out what modules were used on a particular site. Is there a way to find out what modules are being used on a site via the source code or via another module/method?

I've looked at the source code for a Drupal site I like, but I'm not seeing any references to modules.

Thanks for the help.

Pxl