Which PSU should i get/psu requirement for sli

Hey, i am currently in the process of building a new pc. I already bought a Asus P8Z77-V LK mobo, 1tb hdd, 16gb ddr3 ram, and a dvd writer, and also a evga gtx 550 ti 2gb video card. i plan to get an i3/i5 cpu. the question now is, i plan to sli (get a second video card) in the future, and was wondering which power supply should i get from my current items? I read something about the 12v amp requirements, and not sure which psu is good enough. My budget is around 75-85CAD, hoping for black friday for psu. but what is the recommended psu 12v amp for everything tho?

i found these, not sure if they are good enough:
http://ncix.com/products/?sku=71919
http://www.ncix.ca/products/?sku=75200&vpn=TR2-700W&man...
http://www.ncix.ca/products/?sku=63239&vpn=P1850SNLB9&m...