I use a pair of wharfedale valdus 500's which are around 10 years old with an arcam alpha 9. Which play dubstep well. However to play real deep you need a sub. I bought a sw150 for £70, works well for the price, retail was around £250ish
You can get the newer version of my speakers - wharfedale xarus 5000 new for £140 from amazon which is a good value
That plus a good amp and your set
Is this for parties or home listening, how loud do you want it?
If you wanted just really low bass just get bookshelves and a sub, but if you want real midbass slam get some decent floorstanders, maybe add a sub later??