PixelGenius' PhotoKit Color was highlighted in the May 2005 Shutterbug. They discussed using it for One-Click Split Toning and other creative effects. (pages 165 abd 166)
For split toning you do not need to make any selections. They are made automatically. Effects are in a new layer leaving your original untouched so you can feel free to experiment.
Available for MAC and WIN. Cost is $99.95. See at
http://www.pixelgenius.com.
I have no connection to this company, but have used some of their other products and liked them.--Rene