There are many thousands of plugins for Photoshop. They are all over the internet and from hundreds of companies. There are also lots of free ones. If you just type
into Google, you'll get over 2,000,000 pages. Take a look at the first 30 or so listings and you'll find more than you'll ever what to use.
A couple that I like and use all the time are linked to on one of the pages of one of my websites:
I also think highly of the NIK Color Efex filters and the AutoFX filters (Dreamsuite, PGE6, Mystical Lighting)