There are probably too many free plugins for PSP to mention here but I will mention of as PSP9 doesn't have a Highpass filter which is useful for tileable textures and the free Mehdi one I used previously works in PSP8 but not PSP9.
It is called the Highpass Sharpening filter which is a popular method of sharpening an image that does a more natural job than just 'sharpen' but if you check the 'View Highpass' box you get a standard Highpass.
