Sub recommendations for HT

What are some good subwoofers in the $500 - $800 price range for a large room. I'd like to keep the sub itself as small as possible though. I have considered the Sunfire subs but they are a little out of my price range.

Thanks for any help.
I thought the Sunfire junior sub will fit your price range, and possible a used Sunfire also -- I might be wrong. ACI Titan used to offer a kit package that costs about $700-800. Both Sunfire and Titan II are good with bass for music and movie. I recommend doing some hunting and get a decent sub, then you will not regret. Have fun!
Definitive Technology Subwoofers make great HT subs, and you can find them for pretty cheap.

I used to have the Definitive Technology Prosub 200, 12in driver 250rms, brand new it cost 549.00, never had any problems with it and it was a damn fine performer. Personally i liked it better than the equally priced velodynes. Worked pretty good for music, but excelled in HT.

Unfortunatly i had to sell it. WHen i rebuilt my HT thats where im going for my bass. But i will probablty splurge for a SUPERCUBE
Thanks for the input.

I have been looking at Velodyne ans Sunfire in the used market, but have not made a decision yet.
If you haven't purchased a sub yet, what I gathered from talking to Mike/owner of ACI, is their 'Force' sub, $750 is the same sound quality as the Titan II with lower output. I was willing to spend on the Titan, but Mike suggested the 'Force' for my lower output needs. I'll be using the sub mostly for music and the occasional movie.

Side note. I've never known of a more customer friendly company.