Full Flipper Fidelity.

Line the sides of the PF glass with electrical tape so it fits a bit more snug because it thumps! So the glass rattles

Oops. Just read "powered" sub. Pretty much any Sony or Polk will do the trick

I've heard a bunch of em' and they ALL sound great!

Polk Audio PSW10. $90 from amazon, free shipping. It has speaker and line level hookups so you can connects lots of pins.
FF speakers are great for the backbox and include custom spacers. The biggest difference is the sub, since sound on pins is compressed and you lose some of the high frequencies. That being said, I did use some Pioneer 4" 2-way speakers on an IM and didn't use spacers, just mounted them flush with the grille, and I actually thought it looked cool and the sound was incredible.

I have two of these. Spectacular for TRON and AC/DC. I disconnected the 12" stern sub and did this on AC/DC and it is night and day.

I believe it. I thought a cabinet sub was "good enough" for SM, but once I hooked it up to the Polk, wow. I have used it with Tron before (and will again soon) and it was just crazy. Even had a neighbor complain, too much bass. . I really find it hard to believe these powered subs are so cheap.

+1 for the Polk. Every game should get one of these, and with the polk i believe you can hook up two at a time (but have not tried it yet)

You guys in the US are spoilt. Just looked at the same Sub on Amazon UK and it is £344 ($516). Just have to look out for something else on ebay which is equivalent and cheaper

Full ff kit and Polk PSW10, and like fattrain says you're going to have to experiment with tape to prevent glass rattle. It's really bad on this game. I had to add electrical tape in some spots and 1/4 strip of 1 sided sticky foam along the back edge of glass under the rear plastic channel. I picked up some from the window dept in lowes. Have to slowly install the glass with sliding a gift card/credit card under the channel and babying the glass in. Pulling and re-installing the glass is a pain, but no rattle whatsoever. I got the game vol set to 50.

I'd do ff tweets and a polk sub for acdc too. I didn't notice an issue with glass rattle on acdc.