I just bought my second 780ti both are this exact model: EVGA GeForce GTX 780 Ti Superclocked w/ACX Cooler 3GB GDDR5 384bit Dual-Link DVI-I DVI-D HDMI DP SLI Graphics Cards 03G-P4-2884-KR
 
How big of a PSU should I get? Ive heard anywhere from 750 - 1000w
 
Thanks.

I currently have
CPU: i7-3770k
Ram: 16gb
and a 650W PSU
 
Im not sure how much overclocking I will do but I am tempted to grab this because its $109 with coupon code: 
 
EDIT:
apparently links dont work on this forum. But newegg has 

SeaSonic X-1050 ( SS-1050XM2 ) 1050W ATX12V / EPS12V SLI Certified CrossFire Ready 80 PLUS GOLD Certified Full Modular Active PFC Power Supply New 4th Gen CPU Certified Haswell Ready

 
for $109

Buy SuperNOVA 1000 G2 or 1000 P2.
With P2 you can Enable Eco Mode and fan will work only during high load. 

I'll usually agree with Sajin on most of his posts, however on this one I strongly disagree. Your 780Ti's do consume a little more power than my 970's but not THAT much more. Running Futuremark Fires trike on extreme mode, my system which includes:
i5 2500K@ 4.6Ghz 1.335V
EVGA P67 FTW
4x Sticks DDR3 1600
2X overclocked GTX 970's
DVD Drive
3 Solid State Drives
2X Western Digital Raptors
4x 120mm fans
Intel Self Contained Water Cooler
--------------------------
This system peaked 496W!
yes if I was to totally load the system running Prime95 & perhaps Furmark at the same time, it may peak a little higher, but not that much more. you will NEVER cap your system and every part in it at 100% at any given time in your life. personally a good quality 750W PSU should be more then sufficient. My advice: buy a wattage meter, and monitor your power usage yourself and be your own judge. It's not like we're talking about a GTX 480 here.....those are total hogs!
 
P.S. Crysis 3 Seems to draw more juice than all other games I personally play. Reached 524Watts.

Even with a i7 3960X overclocked to 4.6GHz a full system with SLI GTX 780Ti's won't break 620w while gaming.
http://www.guru3d.com/articles_pages/gtx_780_ti_sli_geforce_review,4.html
 
A solid 850w would do just fine. Something like the EVGA G2 850w. 
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story4&reid=377
 
Newer power supplies can actually take full load, unlike the old ones that had bad ripple suppression after 80% load... which is what causes degradation of the PSU from heat. Quite a few of the new PSU's that are Gold or Platinum certified can handle full load far better now than they ever could.

I'm really impressed with the newer EVGA PSUs. I'll probably be buy one before too long.

Always shoot for above the bare minimum that you can go with.... Trust me over time PSU's degrade, esp if you are pushing that puppy over its eighty percent efficiency constantly, its just a matter of when the capacitors inside will go ok I give up, and pop... I always make sure my psu's even at max peak load I am under that eighty percent efficiency only using seventy to seventy five percent of that psu's recommended efficiency rating with plenty of watts to spare so even after years of use I can still depend on that psu if need be.

donta1979
Always shoot for above the bare minimum that you can go with.... Trust me over time PSU's degrade, esp if you are pushing that puppy over its eighty percent efficiency constantly, its just a matter of when the capacitors inside will go ok I give up, and pop... I always make sure my psu's even at max peak load I am under that eighty percent efficiency only using seventy to seventy five percent of that psu's recommended efficiency rating with plenty of watts to spare so even after years of use I can still depend on that psu if need be.

You might want to read the review I posted. That's starting to be a rule of the past.

Vlada011
Buy SuperNOVA 1000 G2 or 1000 P2.
With P2 you can Enable Eco Mode and fan will work only during high load. 

+1