I have two PCs set up just now, and I'm running them with a Microsoft Natural Ergonomic Keyboard and the 4000 Logitech Ultra-Flat Keyboard.
For extended periods of work, I automatically default to the Microsoft keyboard. (Armrest, Split Key System, angle of inclination... it just feels better. Then again, I've been working on split/natural keyboards for the last several years. Some people can't STAND them.)
On the other hand, the Logitech Ultra-Flat Keyboard is probably one of the PRETTIEST made-for-PC keyboards I've ever seen. Small, discreet, angled fairly low, excessively reminiscent of a Laptop Keyboard. Comfortable to type at (may seem cramped to people used to huge keyboards, but ideal to people that wish their desktop keyboards were a bit more like their laptops...) and pretty. And black, to match your Hackintosh