I've long been a fan of Picasa -- the free photo management program. I've mainly used it to crop my photos (THE most essential tool for me,) to straighten them, and occasionally to up the color saturation a tad.
A recent version of Picasa (free download -- just google Picasa) has added a number of new ways to fiddle with your photos. The picture above of Eddie has been given the neon treatment; the clematis has been made to look like a pencil sketch . . .
Blue neon for the iris in a canning jar and the single white iris below has been treated to a heat map . . .
Oh, what fun I'm going to have!