The example would be for OS X, but you could easily adapt it to whatever you wanted.

A couple of the punctuation keys have been moved, which isn't immediately obvious.
Backspace and Delete are now next to each other, just because it always bothered me that they weren't.
Page Up, Page Down, Home and End have been shuffled into an inverted-T, so you can use them for navigating text more intuitively (Top of Doc, Bottom of Doc, Start of Line, End of Line).
I added a Shift Lock key, just because I always wanted one for working with code, and moved CapsLock to make way for a decent sized Function key. The lowest two rows have symmetrical modifiers now too.
Media controls are along the bottom, mostly because function keys are along the top. Screen and Keyboard brightness are in the new inverted-T.
It's pretty unlikely this will ever be built, but maybe some of the ideas will be influence someone.
Thanks for looking.