You'd basically be entering the arena of high-end miners - and while some of them give positive ROI, a bunch of them are only available by pre-order and you have to trust that they won't be delivered late (with difficulty increases messing up any chance of positive ROI).. you're also taking a gamble with the difficulty in general, and of course the exchange rate.

Make sure you read the horror stories about several companies delivering miners that underperform, arrive severely damaged (dislodged coolers, dislodged components, huge dents in chassis), miss parts completely, go up in smoke (literally), and offer nothing but excuse after excuse when it comes to setting things right.

If that hasn't scared you off, look up some of the miners available (see the Hardware subsection), find their claimed (where possible, actual) hash rates, cost (including shipping, etc.), power use, time for delivery, all that.. then hit up a mining calculator (there's a thread that lists a bunch), and run a few different scenarios (difficulty increases, exchange rate if wanting to calculate with fiat), then see if it's worth the risk to you.

Chances are good that you'd be better off buying an Scrypt miner, mine some altcoins, and sell those - but even that's getting to where manufacturers are starting to flood the market, so don't take that as advice.