Screen Paver
(Furiously busy here, so entries may be shorter and perhaps sparser than they usually are.) I picked up a nice little screen saver program that doubles as a simple slide show presenter: Screen Paver. It's technically a screen saver, and you can set the program's parameters through Control Panel's Display applet, as with any screen saver. But if you set the time interval between images to 0, then it waits for a mouse click to change images.
From the Display applet, you enter several different directories containing images, and Screen Paver will pull images randomly from all entered directories and display them at the specified interval. It will also play MP3s pulled randomly from a directory if you want music during your dead-times.
One reason I like Screen Paver is that you can individually select among 32 different transition effects. I find some of the available transitions annoying, but each one has a check box, and you can un-check whatever transitions you don't want.
Small, works as advertised, and precisely what I needed, right when I needed it. $12.95. Highly recommended.