Here is a link to tons of free filters:
http://www.ravingconcepts.com/plugin_filters.htm

and here are more free filter links:
http://bmath.net/dc/index.html
http://www.redpawmedia.com/
http://www.angelfire.com/linux/pip_plugins02/
http://www.angelfire.com/linux/pip_plugins05/
http://www.geocities.com/image_classrooms/IRFilters.htm
http://www.btinternet.com/~cateran/simple/
http://joellebarn.ifrance.com/filtres.htm
http://pspdutch.info/download/filters/filters.htm

These are good for both PS and PSP so Enjoy!!