XT - 83 keys, convertible with an XTant kit and USB capsense controller; ~$50
Show Image
(http://clickykeyboard.com/2012/may26/016)
AT - 84 keys, usually modded to ANSI and adding Alt keys by replacing the long space bar with a 7x one; ~$100
Show Image
(http://i45.tinypic.com/15f61t.jpg)
F122 - most common Model F, convertible with a Teensy / Soarer to USB; ~$80
Show Image
(http://www.seasip.info/VintagePC/Images/6110344.jpg)
F50 - all metal case, convertible with a USB capsense controller; ~$100
F62 - all metal case aka Kishsaver/Tinsaver, convertible with a USB capsense controller; ~$200
F77 - all metal case, convertible with a USB capsense controller, only three known examples; ~$300
F107 - all metal case, convertible with a USB capsense controller; ~$200
Show Image
(http://kkraftonline.de/Museum/data/images/4704%20Keyboards%202.jpg)
There are less common variants of many of these boards as well.
Makes my post look nub. I'm going to use the i was at work card, lol.