You can easily install additional Presets into Photoshop. Presets include Brushes, Gradients, Patterns, Actions, Styles, Curves etc…

Presets are Located Here:

Mac OS X:
~/Library/Application Support/Adobe/Adobe Photoshop/Presets/

Windows:
C:\Program Files\Adobe\Adobe Photoshop \Presets\

Please note the following:
Photoshop brushes have a .abr extension. Put these files into the Brushes folder.
Photoshop gradients have a .grd extension. Put these files into the Gradients folder.
Photoshop brushes have a .asl extension. Put these files into the Styles folder.
Photoshop brushes have a .pat extension. Put these files into the Patterns folder.
Photoshop brushes have a .atn extension. Put these files into the Actions folder.
Photoshop curves have a .acv extension. Put these files into the Curves folder.

Lastly, remember that if you install or create new presets it’s always good to back these folders up. I have mine backed up automatically with Jungle Disk.