There are three key features I want to see in an HTPC keyboard:
1. Portability - the smaller the better, all-in-one or at least a keyboard and mouse in one.
2. Durability - it needs to last me a while.
3. Usability - easy to use and fast to setup.
I have tried several small keyboards that are supposed to be - according to the manufacturers - well suited for a HTPC. Finally, I have now found a product I can recommend. The Magic-Pro ProMini Wireless Keyboard, sold by Pyramid Distributions. This keyboard also works great as a wireless presenter.