There are several great ones -
I have the Cubic Grizzly - this will be my first winter with it - so I am looking forward to the cold. I have heard they work great - and saw one in a smaller bus that heated it up nice and toasty. There is the Cub and Grizzly.
I friend just had a Tiny stove installed - and says it's great.
You can get some smaller ones at ACE Hardware - or local hardware / wood stove places - or craigslist.
Just do your research on installing and venting it! The Chimney / Pipe is easy to install - but very stressful to think about - especially drilling through the ceiling / roof!