For my keyboard, I use a Kinesis Advantage. If you read the Amazon reviews, you'll see quite a split of opinions. It's really a wonderful keyboard, comfortable for extended use, with hardware remapping so you can move keys that you need to places where they're more useful (e.g., I've moved the Escape key onto one of the thumb buttons).

Pretty much the only problem with it is that the firmware has a few bugs which the vendor seems unwilling/unable to fix. (When I asked about this a few years ago, they promised they were going to develop new firmware and would contact me as a beta tester when it was ready. So far, nothing.) These bugs only manifest themselves when you're doing things like holding down a modifier key and using the arrows to select text (there will sometimes be an extraneous keypress that blows away the text that you were carefully highlighting, so you have to be on the ball with the undo command).

The only other caveat is that it takes about two weeks to teach yourself to type on this thing. Many of the peripheral keys, like the tilde, are in very different positions relative to a normal keyboard. You just can't expect to buy this thing and be up to 100% productivity without retraining yourself.

Now, I just wish they'd come out with a new model with some sort of integrated pointing device.