Identifying compatible bottom brackets It's time to replace my bottom bracket.  I have an FSA MegaExo with what appears to be a part ID of BB-7100.  There are various markings on the face of the cup, as shown in the attached photo.  While this bottom bracket has done well enough, I'd like to look at other options and get the best price I can.  But I'm not sure what I need to match up to ensure compatibility.  I see, for example, that one measure is 24mm, which appears to be the diameter of the hole for the the splined shaft.  Presumably the width of the bottom bracket shell also matters, but it appears that there are bottom brackets that are made to accommodate various widths.
So, in short, what do I need to match up to ensure that a replacement will fit?  Thank you.
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.