Fruity Loops, Image Line FL Studion Edition.

FL studio. buy HERE

Ableton. buy HERE

And a lot more.

Reason is good too.

Or you could buy a mixer and a bunch of synths/pads/DMs and be a hardware fgt.

I use FL Studio, But if you want to make really good dubstep, you have to download/buy more plugins and VSTs, such as Massive, Sylenth, WOW filter, etc. etc.. lots of things.
If you don't have a lot of money (or don't want to crack everything) you should use Ableton, that already comes with lots of useful things

FL Studios has a demo version which you can try out before you buy it...

this guy (I linked to a video where he shows you how to make wubwubwub bass) does tutorials on how to make dubstep in FL Studios and he sometimes links to free plugins/sound packs.