This is a short tutorial on how to make 3D anaglyphs with Photoshop. Please note that I don't have a degree in 3Dology or anything- I just figured (it out) when making pictures for myself, so any corrections or suggestions are welcome.
Quick background info for those not in the know: anaglyphs are the 3d pictures that require red/green or red/blue glasses for viewing. Someone else can probably list some commercial programs or plug-ins that will help you achieve this effect, but I've gotten good results just using photoshop. These instructions are for making full color, left-eye-red right-eye-blue images.
Get Two Pictures
Step one is to get two pictures of your subject, taken at exactly the same time but from a few inches apart. An easy way to do this is to get two disposable cameras and tape them together side by side; the two lenses (and the two viewfinders) will be about as far apart as your eyes are, and that's crucial. To take a picture with your double-camera, just point it at you subject, hold it _very_ steady, and press both shutters. It's not perfect, but it's cheap. :)
Digitize the Film
Step two- develop your two rolls of film and digitize the pictures you want. Getting a photodisc made from the negatives would be great, but you can just scan them in with a flatbed scanner as long as they're straight- if one of the pictures is scanned crooked then they won't match up in photoshop.
Step three is the photoshop work- make a new photoshop document, and paste the two pictures in as new layers. Figure out which picture is the left-eye picture- it's the one where everything is shifted to the right (meaning it contains stuff on the left side of the frame that isn't in the other picture). Hide the right-eye picture for now. Making sure you have the left-eye layer selected, open the "channels" palette. It should list RGB, Red, Green, and Blue channels. Click on the Green channel, choose "Select All" from the Select menu, and then fill it with black. Fill the Blue channel with black too. Then click on the RGB channel, and go back to the "layers" palette. Repeat the last step with the right-eye picture, only this time you only want to fill the red channel with black; leave the other two channels alone. Move this layer in the layers palette so that it is in front of the left eye. Magic time- Make sure you have the right-eye layer selected, and look for the drop-down menu at the top of the layer palette which lists the compositing method for this layer. By default it will read "Normal"; you want to click on this drop-down and change the method to "lighten". What you will now see is the blue/green channels from the right image, which are only visible through the right lens, superimposed on top of the red channel of the left image, which is only visible though the right lens. In order to get a proper 3D effect you have to line up the two images; you'll notice as soon as you try that they won't line up exactly, because they were taken from different angles. To get them to line up, try one of these methods: