Continental will take one per physical jumpseat. Continental Express will take as many as there are open seats in the back. So will CommutAir, which does Continental Connection throughout CLE and the northeast.
Unfortunately Continental charges its employees to non-rev, making it more likely the jumpseat is taken even on open flights than on US Airways or Delta, where there isn't a per-flight charge. Sometimes with the cooperation of the gate and captain they'll sneak more than one jumpseater on, but I wouldn't plan on it. Still, worth a shot.