There are some plugins that do this, but I want to link WordPress Plugin Credits (WordPress Plugin) by ShibaShake. Probably because it’s pretty well documented, but additionally because of the spirit behind it.
If you have a self hosted blog, it will display credits on a page of it’s own for the plugins used. This not only gives credits to the plugin authors (which is generally a thing most self proclaimed webmasters on their sites forget to admit) but also shows others how you created or extended your site. Next to credits this is imporant because many of your sites users might ask themselves how you could build a feature rich site.
As there is a magnitude of plugins to select from, it’s not always easy to find out which ones are doing the job. Plugins like the one linked can help interested visitors to find out more about how you made your worpdress driven site.
Full Disclosure: WordPress.com (the plattform hosting my blog) is not showing which plugins it makes use of concretely.