If you're thinking of a sealed box, one of the best subs for that is Image Dynamics IDQ v3. 1cu ft sealed box is about perfect for it. It's a great SQ sub and good sensitivity. Also, right now I run about 600 honest watts RMS to my Infinity Kappa 120.9w subwoofer for over a year. These are some of the most overlooked subs. 1cu ft (net) filled with polyfill is about perfect for these. While they're rated for "only" 350watts RMS, the 17mm xmax excursion and solid beefy construction suggest otherwise. They have very low inductance, which promises good sq, and there is a switch to select between 2ohm and 4ohm impedance (someone suggested this is due to a very unusual triple voice coil design). It gives nice, very tight sounding and transparent bass (if your trunk doesn't have any rattles) and will vibrate your mirrors without breaking a sweat if you push it hard.