Very nicely done. You must have studied a lot if this your first build.
Regarding the power supply, even with the GTX 670, you can go as low as the Antec Earthwatts Green 500W; that'd cover the overclocking the processor as well. If you want even more extra, there are the XFX 550W and Seasonic 620W. I don't know how much power the GTX 660 / 660Ti is going to use, but it won't be more than what the GTX 670 uses.
The only reason to consider more wattage would be if you are interested in SLIing the grpahics card. With 2 x GTX 670s in SLI, the 650W version of the Corsair Enthusiast or Professional Series might be okay, but, it's better to get the 750W version. However, since you are getting a lower tier card than the GTX 670 here, the 660 / 660Ti, 650W would be enough for SLIing the card that you are getting.
Anyway, if you are interested in SLIing down the line and you can easily afford the 750W, the 750W isn't rediculously overkill.
i7-2600k @4.5GHz, Scythe Mugen 2 Rev. B, 8GB DDR3 1600, GIGABYTE Z68XP-UD3P, GeForce 9500GT, PC P&C 610W, Plextor M3 128GB, Hitachi GST 7K3000 x2 & WD Black, ASUS DVD & LG Blu-ray Burners, Win7 Pro x64, CM 932 Case.
HTPC + Media Server: http://www.eggxpert.com/forums/permalink/5855/836221/ShowThread.aspx#836221