I was thinking a Betta too as long as your work doesn't mind you doing water chances at your desk.

Also a turtle is nice idea too, a small land turtle of course. I have my Mel, small little guy who lives in a clear small like storage container (no lid of course). No tank to worry about there and there's something calming about raking his sand bottom and fixing him his little island up. I've had him over 2 years now, no problems ever.