I just released a freeware codewheel generator for Win XP/Vista systems.
The program generates six different types of wheels, up to 8 tracks each, at any practical number of cells per track. You can print out the wheel, at designed size, on any home inkjet or laser printer. And printing is a snap. If you design a three inch wheel, it will automatically print at three inches in diameter. No fooling around with printer driver settings. The program automatically adjust for printers having non-symmetrical horizontal and vertical resolutions, too.
You can use these wheels to build your own optical encoders, at pulses per revolution limited only by your printer's resolution and mechanical fabrication skill.
Although the program can generate wheels for just about any application, including absolute position and quadrature encoders, one wheel is of particular interest to robotics hobbyists.
The single code track with index track wheel can be used to fabricate an optical encoder for any application where the direction of rotation is known. This would be ideal for wheel speed and position sensing, odometry, navigation, motor speed and position control, etc.
The beauty of this design is that there is no need for precise positioning of the photodetectors. You could even fabricate a "quick and dirty" optical encoder using nothing more than a couple of LEDs, phototransistors, a simple mask, and your hot glue gun.
The program is available for download from my page at http://www.mindspring.com/~tom2000/Delphi/Codewheel.html
Go forth and build!