Corsair RM 750w
XFX Black 750w
Seasonic X-serie 750w
(They are 5 y. warranty in my country.)
CPU : i7 4770
MB : ASUS H87-plus
VGA : GB GTX 770 2GB
RAM : Kingston HyperX DDR3 4GB*2
HDD : WD Blue 1TB.
PSU : GW 600W
CASE : CM 690 III
CPU-Sink : CM V4 GTS
Case Fan : CM SickleFlowX Red LED 120*3 + CM Megaflow 200mm + Termalright Xsilent 120mm + CM 80mm
If i'm going to SLI my gpu in the future, would the 750w psu is enough? (770*770+new MB)
A quality 750W PSU should be sufficient. Out of the three options that you listed, I pick Seasonic, who is arguably the best PSU OEM in the market today. XFX is also good because their OEM is Seasonic.
The Seasonic X and the XFX are the same unit internally so go with the cheaper of the 2. Seasonic makes all XFX power supplies. The Corsair RM is likely a very good unit as well but the Seasonic X is about the best series on the market right now.