Currently for BTC ASICs I would recommend buying in stock 180GH Antminers, from the distributor closest to you. Or keeping an eye on developments from AsicMiner who always had a sell from stock policy.
If you want to get ahead on scrypt altcoins, check out the Titan from KNC, (Link in sig) 100 M/h scrypt miner, the power of 150 GPUs for the price of about 20. KNC has thus far been the most reliable (least late) of all pre-order ASIC manufacturers.
GPUs, welllll, buy used as cheap as possible... they've got about 6 months I think before they are totally pwned by the scrypt ASICs. Now when the ASICs ran them out of BTC the top end cards were going for only $50-100 in the panic selloff before LTC got very popular again and Doge happened, so on a new card, getting even a quarter of your money back on it is "somewhat hopeful" when everybody is trying to dump GPUs at the same time. You can hold onto it and hope to get half or better when the next non-scrypt doge comes along, but I think you'll be "lost in the desert" for several months as it were.
scrypt difficulties will go insane yes, in BTC the immediate effect of ASICs coming online was that the price went up by 10x, then dropped by half (Back to 5x Jan13) then up 10x again. This rise kept the GPUs "on" for another week, then another week, then another week, until finally they were outclassed.