This site proposes several free plugins (+1 shareware) which support Photoshop, Corel PhotoPaint,Paint Shop Pro, RealWorld Paint, Photofiltre Studio etc... You can find a non-exhaustive list of compatible hosts, here.
I'll release progressively a 64 bit version for all my plugins. You can see on this page, which plugin have a 64 bit version available. I'll try to improve some of them.
Major Update: Plugin HSL 2.
More flexibility with the chroma.