I know The 7950 is the most efficient in (MH/s)/$/watt... but I have contractual access to unlimited free power. I'm already using the power anyway so the marginal cost of the power is actually zero. Is there a machine I could build and turn a profit with at this point? Litecoin is not the most profitable Scrypt coin to mine now, so don't assume I'm mining Litecoin. The asics coming out "soon" might be a concern, if they actually even come out soon, but its my understanding that they are good for being low wattage, whereas the hash/dollar is similar to GPUs still. Assuming I could be confident that a Scrypt asic manufacturer is trustworthy enough to buy from, I wouldn't be opposed to doing that, but thats really a pretty big gamble, unlike ordering a bunch of parts from amazon/newegg on cyber monday. Also I'll be able to resell GPUs, so even if this becomes non-viable after 6 months or so, I'll be able to recover a decent chunk of my investment. I say "unlimited budget" meaning I can fully saturate a motherboard with GPUs or purchase an asic without an issue, whatever the most efficient is.
There are a few other GPUs that do a bit better according to this list:
I think this is just based on user feedback to the Wiki. The ones with a lot more khash/s are multi-card setups.
Really if you have free power you should mine with whatever you can afford, then add more cards after you have coins and have sold them. There are instructions on a cheap multi-card system here:
Unfortunately many of the parts referenced are difficult to find - they sell like hot cakes! The R9 280X is equivalent to the 7950 and is usually cheaper.
Don't forget that there are dozens of scrypt based currencies and mining the most profitable one over LTC can net you a lot more income. I can't post any more links here but google multipool or check www.multipool.in for a start.
Also don't forget that if you put in a nice 4 or 6 core processor you can also do CPU mining for PrimeCoin, QuarkCoin or ProtoShares.