The highly regarded Nik collection of plugins for image processing used to cost many hundreds of dollars.  Then Google bought them, and they came down to something like US$125 (what I paid three years ago).

Now the Nik plugins are free, and highly recommended, even though they are probably not going to get updated any more.  They work with Photoshop, Lightroom and Aperture. You can go here to find out about them and download:  https://www.google.com/nikcollection/

Even better, there is now a free set of online videos providing training on the Nik plugins.  Go here to register and view the videos online or download them: http://greylearning.com/courses/nik-bundle