You picked a card that will play any game very well, good choice. And the card determins the power supply needed since its the most power hungry part. Running 2 identical vc's in SLI or Crossfire is done when the user wants to increase the graphics hp w/o buying a different bigger vc. Having one card is easier than getting 2 cards and it's software to cooperate w/each other, so that's what I would recommend here, 1 card. If you ever needed a bigger card, it would be explicitly be for games since the rest will be smashed by the single 560ti, and as mentioned that single 560 ti plays any game real well.
Which brings us to the mb. The one you chose runs 1 vc @ x16, or 2 @ x8 each. Good for 2 vc's. Altho you can use that second slot for some other component, you could also get a nice mb that only runs 1 vc @ x16 and save a bit of dough.
Back to the ps. 750w is enough for 2 vc. So If your going to go the single card route, less wattage would be enough and probably more efficient. Check the Power Supply sticky here. It has reccommends for whole system amps based on the vc. Corsair/Silverstone/PC Power&Cooling/Antec/XFX/Seasonic are the brands to get.
Western Digital Black - Spinpoint F3 - Seagate w/7200.12 firmware.
Those are the top 3. With the ssd for the os and programs, maybe games,, the hdd would be for everything else - docs, photos, videos, etc.