That is true, it was easy for me to sell the 1800. I think it is because of affordability.
For decent subs, it depends on how much you want to spend obviously, for $299, the one James reviewed not long ago seems like a winner:
$300 RSL Speedwoofer 10E Subwoofer Review
At the higher price point, there are just too many to choose from so I would just pick one from SVS's. I bought their cheapest model recently for one of my 2 channel bookshelf speaker based stereo system. It is the SB1000 Pro and am happy with it. If you need more volume and extension, then should start with the PB2000 pro and go from there.
Again, there are many to choose, you probably should go through those James reviewed.
James Larson