I was using Wallpaper Slideshow, but there are a few things I don't like about it.

The features I need are:

-Change wallpaper each time windows starts
-Also change at set intervals
-Select image randomly, but not the same one twice before it's gone through all of them
-Change wallpaper with one mouseclick
-Be able to select whole directories INCLUDING SUBDIRs that have pictures (I've got mine sorted by the artists who made them)
-Strech all images to fill up all the screen
-Not slow down the computer terribly
-No bugs! blah

I found 'Wallchanger' which is kind of nice I guess, but I can't find one working serial for it...