Choosing the right PSU

Ok guys I have decided what cpu, motherboard, gpu, storage and ram I'm going to use but I dont know what the right PSU would be for me. I will list the spec below so you guys can inform me what would be best but how do you calculate what would be best? Specs:

-Gigabyte 990FXA-UD3

-AMD Phenom II X4 965 3.40 Ghz


-Kingston Technology XMP Beast Series 8GB 1866MHz DDR3

-WD Caviar Black 1TB 7200 RPM

Now this build will be a continuesly upgrading rig so I would like to have  PSU which will work for what I have now but also be future proof. I have 1 machanical drive at the moment but I'm planning to buy another and set them up in RAID 1. I also plan on buying a SSD (not sure what capacity) to store my OS on. Another possibility which might not happen is a friend will be selling his almost new GTX 660 Ti like mine so I could possibly maybe potentially have dual GPU's one day.

Thanks in advance!

Something like the Corsair TX750M would be ideal for a build like your current one.

But if you'd like to future-proof, so you can add, oh, say, another graphics card, or do some overclocking, or I don't know, then you'd need something with more power, something like a NZXT HALE 90 1000W.

You could still do a SLI build with the TX750M, maybe... But with overclocking and all that going on, it might be cutting it short.

I'd most likely just go with the HALE 90 and be done with it.

Don't forget, when buying a PSU, keep an eye out for 80+ Certified, a good brand (XFX, Seasonic, Antec, Corsair...), and modular can be helpful. 

Hope this helped :).

Thanks man, really helpful :) I was looking at a 520 W PSU