If you can handle a large sub, look at Hsu, Outlaw Audio, SVS, and Monoprice Monolith. If you need a smaller sub, those manufacturers have some medium sized offerings, and also look at MartinLogan and Paradigm Defiance X series. I have spent some time with the Paradigm Defiance X12 recently, and it is very punchy for it size, although it is just a tad over your budget.