Contour Perfit Mouse Optical is a 3-button optical mouse. The only problem is that it's $110. http://www.contourdesign.com/pmo/

HP seems to have done it! HP Site
Froogle Link
Apropos of http://www.scarydevil.com/~peter/io/mice.html and similar
rants in other places:

HP part number DY651A is a three-button (no wheel) optical mouse;
it attaches by USB and seems perfectly normal in every respect.  The
oddest thing about it is that it's black.
-- A post in the network that shall not be named.

Where are all the three button mice?
I don't think I'm being unreasonable.

All I want is a three button optical mouse.

I don't care if it's USB, PS/2, Serial, IR, Wireless, Wired, RF, Bluetooth, or even if I have to plug it into a parallel port dongle with a separate power supply. All I want is a three button optical mouse.

But Peter, there's three button optical mice all over the place! Five bucks from three thousand different resellers of Logitech and Belkin and Kensington and Microsoft...

The problem is, there aren't. There's two button mice with scroll wheels all over the place. If I wanted a scroll mouse I'd be set... you can hardly find a mouse today without a scroll wheel. The problem is, a scroll wheel is a little fiddly thing that needs to be pressed precisely if you're not going to twitch the wheel by mistake and end up pasting text 5 lines from where you thought you were. Even with scrolling turned off, it's harder to hit that little tiny button easily.

Half an hour of work with a scroll mouse, and my right wrist is a knot in the center of a bar of pain from my fingertips to my elbow.

Why are you using the scroll wheel to paste?

I'm not, I'm using the paste button to paste. I'm using UNIX, the X Window system, it's the same window system Linux uses. In classical X applications the three buttons on the mouse are "select", "paste", and "extend selection" (which you can think of as "copy"). This combination allows you to use a mouse by itself to select and copy objects without using the keyboard and without "dragging" the mouse with the mouse button held down. Until they started replacing the third button with a scroll wheel, this let me use a GUI without moving the mouse while holding a button nearly as often, which in turn helped keep my RSI in check.

I know I'm not the only one who needs a three button mouse. Jeff Poskanzer at http://www.acme.com/build_a_pc/other.html says:

I require a three-button optical mouse. These are getting somewhat hard to find. Mouse Systems was one of the original makers of optical mice, since back in the early 1980s, and made a nice simple & solid three-button optical mouse. Unfortunately they got bought out recently and the new owners, KYE International, are making the same two-button mice as everyone else. Logitech and Belkin both make three-button mice, but not optical ones so far.
This comes up as a regular topic when UNIX users gather.

Look, guys... and I'm talking to Logitech and Kensington and Belkin and other companies that make optical mice here... Linux is hot, and getting hotter. Apple is selling UNIX on their Macs now and native UNIX apps want a three-button mouse. Some of you make special UNIX keyboards and mice for companies like Sun. How about it? Three button USB/PS2 optical mouse, call it the "Linux Mouse" (hey, Logitech, that nice triangular 3-button mouse you were selling for a while would be perfect). Advertise it on Slashdot. You'd sell a boatload, and you've already got most of the tooling you'd need: take your 3-button top, your optical base, and replace one component on the circuit board. It'd be easy.

You know it makes sense.

 IO
Lynx-enhanced by <peter&snabla;taronga.com> (Peter da Silva)