There are two kinds of floggers: stuffers and folders. For the stuffers we have the Granite Gear Air Bloc Solid compression sack. Updated from the original white version, the Solid – endorsed by no less than Undercover Brother himself – is a mere 2.7oz of compressatory marvelousness.
The updated Solid replaces the original compression straps with compression cords. Looks funky, works great. Available in four sizes, the medium just held a Feathered Friends Ptarmigan -20F down bag. The Solid knows it's hip to be square, and with a little massaging as you compress your load you end up with a squarish cross section at the end. This fits perfectly in the bottom of your pack, saving a bit of extra room over a round sack.
Granite Gear is all about the sack attack, and the Solid is plenty tough but you'll want to be careful with your investment anyway. There's only so much material in 2.7oz, after all, so just be patient and cinch it tight in steps: crank two opposing cords, rotate, and repeat. Add a knee on top to assist, and you're good to go in no time.