Recs.
Updated
Open-source split keyboard based on the Kinesis Advantage's layout. This keyboard is available as a DIY project. Some commercial clones exist.
Specs
Pros
Pro Ultimate customizability
You can map any key to any position easily using a simple GUI, including making hardware key layers. And, since the firmware is open source, you can modify it to do anything you want. Many of the hardware components can also be altered/replaced by equivalent parts.
Pro More actions for the thumb
Unlike other keyboards, like the Lexmark M15 and Cherry G80-5000, where the only action performable by the thumbs is punching the spacebar, ErgoDox has extra keys placed near the spacebar, within thumb reach. This prevents the thumbs from being a bit redundant.
Pro Split design lets you optimize positioning
You can arrange each side of the keyboard to match your hand positions. Helps keep your body straight and improve your posture. Additionally, you can (for gaming) move the right half out of the way in order to place the mouse in a more comfortable position.
Pro Customization settings saved on the keyboard
With most programmable keyboards, you have to use their software in order to save and reuse your customizations. Using such keyboards on other systems "degrades" them to their default setting. Since with the ErgoDox the settings are saved directly on the keyboard, no matter the system where you're using it, your macros, tap dances and layers are always available.
Pro ErgoDox EZ offers a 2-year warranty
The pre-assembled version offers an extensive 2-year warranty, provided you haven't taken it apart or physically broken it.
Pro Key rows are aligned
Almost all the keyboards have a small row offset (for example, on a standard QWERTY keyboard, the A key is not directly below the Q key. On the ErgoDox, this isn't the case: keys form straight columns. Together with the movability of the two parts you can stretch your fingers straight on, not slightly sidewards. This helps with touch typing, since you just need to stretch your fingers straight onward to reach the key above, rather than stretching it onwards and sideways.
Cons
Recommendations
Comments
Flagged Pros + Cons
Pro Many accessible keys
There are more keys which are easily accessible for touch typists than on the usual keyboards.
Out of Date Pros + Cons
Con Needs to be assembled
This can be fun, but some people just want a working keyboard without having to spend three hours with a soldering iron. It's tricky to find pre-assembled ErgoDoxes, and they're not mass-produced. It is also possible to commission an enthusiast to build one up as well. Some Massdrops of the ErgoDox kit did came with an option allowing one to choose whether to have it pre-made or not.
Con Expensive
Getting a complete kit from Massdrop costs about $400. Sourcing each part individually ends up a bit under $200.