I'll answer this not just for you, but for all those who have never had a 'real' roto-hammer.
Such tools conform to a variety of 'standard' shanks. That is, you are not tied to any particular maker for the bits.
The smallest tools have "SDS" shank bits. Basically a round shank with some flutes and flat spots. These contours allow the bit to be hammered in various directions by the tool, while keeping the tool from hammering itself to pieces.
The next 'size' category has two completely different types of bits, "Spline" and "SDS Max." Like the competing videotape formats, these two types represent different approaches to solving the same problems. While the "spline" type lost the competition, you should be able to easily get a variety of bits from many sources.
The largest category of these tools are 'chisel only" (no drilling), and use different size hex shanks.
Probably the most complete line of bits and core drills is made by Bosch. You'll quickly wonder how you went for so long without the tool.