Just a note, that these filters may not be named what you are used
to seeing them named. I named them however they appeared when
you load PSP, and try to use them in the plugin's directory. Pics are included with each to show how they will appear in the direcotry. For example, DCBook is listed as Frame Filters, because as you can
see in this pic, that is how it shows in the directory. This is intended
to make it easier for you to know if you already have something
or not, before downloading from this site.
These filters are Totally free
Just download these, and move them right into your PSP plugins Folder. (I recommend giving them their own subfolder within the plugins folder)
Free but have Installers
These filters are also free, but have kinda installers. Download, unzip, and double click the installers. Then move the files inside into your PSP plugins folder (I recommend leaving them in their own subfolder, within the plugins folder)(Kang, NVRM, and Ravers, here).