Derek Beals created a LISP routine that will allow you to match the angle of your selected objects to that of a reference object.
"Once the routine is loaded, start it by typing Mag on the Command line. Pick a line you want an object rotated to, select your objects, pick two points from your object's angle, pick your rotation point, and ta-da! The routine has a rotate object at 180 degrees option in case you need to flip your object around."
Notes from Cadalyst Tip Patrol: The routine is simple to use: Pick the object whose angle you want to match, then select the objects to rotate. After you select them all, press Enter. You will be asked for reference points, which create a line of reference in your selected objects. This established line's angle will match the reference angle. Then pick a point of rotation; that point will stay stationary while your selected objects rotate around it.