A lot of good answers already posted above. My contributions to the literature:
Deputy - for shorter turnovers, especially if you like to throw putters (some do, some don't).
Mirage - also good for shorter turnovers.
Mako3 - especially in lighter weights, this'll work well for turnovers. Paul McBeth bags a Mako3 and uses it for turnovers (especially around trees and corners, etc.)
Prodigy M4 - in 400 or 400g plastic, this is an awesome understable disc, possibly one of the best choices out there.
Cobra - especially in baseline plastic, this is a very good disc for turnovers. Rim is not all that comfortable, but is not unlike the Roc3 rim, so is you like that, the Cobra may be your disc.
An no matter what disc it is, you'll need to practice with it to learn and understand how it will fly at different power levels, etc. The turnover shot can be one of the most difficult to master, but once you do, it'll become a powerful weapon in your DG arsenal.