Identifying compatible bottom brackets
There are two things you need to match up for compatibility.

The frame bottom bracket shell
The crank axle diameter and length accommodated

As Adam says the frame bottom bracket shell is BSA/British, also known as 'ISO standard threaded', either 68 or 73mm wide.
FSA Megaexo accommodates a 24mm diameter crank axle, which is the same as Shimano HollowTechII cranks. SRAM GXP is different and uses 24mm drive side, 22mm non-drive side.
You can either get another Megaexo BB or a Shimano unit.