Maybe you've read about these kinds of joysticks in a magazine before - the ASCII Stick L5, designed specifically for RPG players, is made to fit in your left hand.
Sold in a blisterpack-style hanging card (as opposed to a box), the L5 was "devised using new innovations in form-fitting ergonomics for RPG players". The main idea behind it is that you can use just your left hand to move around, talk to people, etc. while your right hand is busy making maps or consulting the hint book. The control pad, Start and Select are on the front side; A and B are on the rear and are hit with your index and middle fingers.
If you think about it, it's really a neat idea but for some reason it sort of falls apart when you try actually using it this way. You can't draw or read a large book very well with only one hand anyway, so you end up dropping the controller, defeating the purpose of making a one-handed controller in the first place. Still, these types of sticks were popular enough that ASCII made versions for the PCE and Super Famicom after this was released.
Still, my main complaint - what are left-handed people supposed to do??!!!
Please do not play platform games with a one-handed controller