I've been reading a bit about APL, and I can't find anywhere to buy one of the old APL keyboards. However, you can remap your existing keyboard to output APL symbols for certain key combinations, which is how I think most people are using it these days.

EDIT: Picture of the keyboard layout: http://www.users.on.net/~farnik/upload/APL2union.gif

Actually you can purchase one here: http://pckeyboards.stores.yahoo.net/adcolkey.html they even provide different colors and special keys (windows key into a meta key etc.) - I have the dark grey one and I love it.

You can also get APL stickers that fit onto any keyboard (I put them onto an hp 1000 laptop even) from here: http://hooleon.com/miva/merchant.mvc?Screen=PROD&Product... for about 15 dollars. They actually work really well - I would advise using a pair of tweezers to get them positioned exactly how you want because one they are on they are pretty permanent!

Wow! Now that looks like a keyboard map for some serious dark programming magic! Now I really want to put on my pointy hat and enter the astral planes of APL!

You can also use J (http://www.jsoftware.com/), which follows the same philosophy but uses only normal characters (all of them, in fact).

Most people are using virtual keyboards, but Dyalog (in the warning on their website) mention that they sell APL keyboards.

J and K both came out of APL ... except they use the normal ASCII character set for their built-in functions. It still seems like magic to me when I saw one line of K execute really quickly and return what takes me dozens of lines of code in another language. Look at the APL/J/K solutions on some of the Project Euler problems. The longest ones are maybe two lines long.