I type on a mechanical, though non-ergonomic keyboard, and like it quite a lot. Specifically a DAS Keyboard Ultimate with Cherry Blue switches. I added o-rings to quiet the report of the click a bit. I have not had tying discomfort in a couple of years since switching to Dvorak layout and going with a mechanical keyboard.

That said. I am not an RSI expert, and can only say anecdotally what I have personally come to like.

I know at least a couple of developers who swear by the Kenisis Advantage - http://www.amazon.com/Kinesis-KB500USB-BLK-Advantage-Contour.... It's a bit pricey, but is apparently a true ergonomic option.

For a straight up nice mechanical with o-rings already installed, the Code Keyboard from WASD is a nice option - see http://codekeyboards.com/.