Lyman M die and Lee universal flare die have been mentioned. Those are the best solutions for cast bullets.
If you are having problems with flat base, blunt-nosed jacketed bullets, there may be another option. The short, blunt bullets can sometimes tilt enough to hit the edge of the seating stem. This collapses the cases, deforms the case mouth, and/or results in very crooked seated bullets. This can be solved by using a "competition" style seating die that has a drop-down bullet guide/sleeve. The advantage to this is you don't need to add a separate step to the reloading process. (But I think the M die is the bomb. I remove the expander from all my rifle sizing dies and use an M die. It's an improvement in a number of ways.)