well i have had the Think Outside bluetooth one for like 6 months, and it has been great. it is really small. i think that they have come out with a new one in the mean time that is a little bit bigger, with a number row of keys. (the one i have doesn't have seperate number keys, it sucked for a programming class that i had last quarter

)
the version that i have is the stowaway bluetooth keyboard. i have only had to change the batteries once. but if you plan on using it a lot (like 5 hours a day) then i would really suggest getting rechargable nimh batteries. they last a lot longer and are obviously reusable.
good luck.
Daniel