Hi,
I just dealt with the keyboard issue myself and decided to go with this neat little
Lenovo HTPC keyboard.
Just tried it last weekend, the range is fine (works across the room even). It's really quite small also, but just big enough that typing isn't too difficult. I like the trackball too, but I use one daily on my workstation so I'm used to it.
The best feature is the dedicated volume buttons, I can use these now instead of putting a dedicated volume control on the outside of my cabinet.
The only issue is that there are no dedicated Function keys (F1, F2, etc.). I was planning on remapping mame to use Alt-1, Alt-2 instead, but haven't gotten that far yet to see if it's feasible.
As far as battery life goes, can't say yet, although it has an on/off switch on the back so I just turn it off when I'm not using it, should last forever at that rate.

It's small enough that I'm considering adding two small stick-on hooks to the side of the cabinet to hold it out of the way, but handy.
Got mine for $40 shipped
off Ebay.
Ken