This is a bit of a plug for Bob Macc's mastering service, Subvert Central Mastering. Basically, if you're looking at hawking your music around DJ's or labels or putting tunes up on myspace / virb / whatever or playing your stuff out digitally and you aren't sure whether you can afford to send them off to Transition but still want them to sound as nice as possible, then this is well worth a look.
It's probably not on a par with somewhere like Transition, and they wouldn't claim to be (Bob gets his own stuff done at Heathmans, I think). But it probably is a shedload better than just running your stuff through cracked copies of vintage warmer and waves multiband and L2 until your ears bleed.
It's also a very transparent and no-bullshit service, not some shady "give us your money then we'll crank your tune through L2 and laugh all the way to the bank" operation - iirc, you send off your tunes to them and they'll send back a clip of the mastered tune for you to listen to and compare with the original before you send them your cash. They'll redo it if you're not happy with the results.
I haven't used it myself (no tunes good enough to be worth mastering so far!) but their satisfied customers include King Cannibal, Martsman, Subtle Audio, Naphta, Counter Intelligence and others.
They also do a mixing service, but that's a) more expensive and b) less likely to be of interest to dubstep producers.
More info, credentials, audio samples, prices etc here: http://mastering.subvertcentral.com/
If people have got questions or whatever, either sign up for Subvert Central and ask Bob there, or post here and he'll probably be happy to sign up and answer them.
) but, I'm sure from what I've heard he can take it to the next level.