On my stereo system I'm using the AGA mps150 -- that's the one that looks a barrel

-- and has 150W. This one has a clever design: the amp and the bass driver are two separate pieces, so you can put them side by side, needing just as few as 7in tall space.
But to be honest, for the money you can get better subs. AGA is superb on the speakers series, but, imho, not so good on the subwoofers.