Well, I like the Rainbow water trap.
I can copy it and it's no big deal since it's not a commerical item. Just a project.
With the water trap, an IR beacon and barcodes on the walls it can find it's way back, recharge, change the water and re-deploy.
Plus they spray pretty smelling stuff and all kinds of neat things.
HA!
I just scored a Rainbow on Ebay for 67 bucks.