On a table saw, cut the rabbet's width (shoulder cut) with the piece flat on the table and against the rip fence. Set the blade to the desired depth, turn the board on edge and against the fence, and run it through the saw.
A router cuts small rabbets in one pass, larger and deeper ones in a few shallow passes. Chuck a piloted rabbeting bit of the correct size and set to the desired depth of cut. Securely clamp the piece to your bench top while routing the rabbet.