If you have the means, and you don't mind an old/used keyboard, I would recommend the IBM Model M keyboard. This is a standard 101 key keyboard with several nice feaures:
- Nice clicky feel
- Large and deep keys that are well separated(easy to type)
- removable keycaps(so you can wash them when they're dirty)
- detachable PS/2 cable(the newer ones don't have this though)
- durable exterior(these keyboards average a decade old and I've never seen 1 dead or had 1 die on me)
- No Windows keys(personally I can't stand Windows keys, but its up to you)
- cheap(since they're old, you can get them real cheap, I got all of mine under 10bux)
Some disadvantages are:
- larger than average, but still smaller than those MS Natural KBs
- heavy(the newer ones are a bit lighter though, but still heavier than normal KBs)