The PSU has got an excellent review:
http://www.hardwaresecrets.com/article/800
It is a bit OTT but it is only around £10 to £15 than some other lower power PSUs and Seasonic do make very solid PSUs.
Having said that there is also the 650W Corsair HX650W for around the same price which is made by Seasonic too.
Of course the following Antec would probably be fine too:
http://www.ebuyer.com/product/159920
http://www.scan.co.uk/Products/650W-...-80plus-Bronze
It too has got a decent review:
http://www.bit-tech.net/hardware/psu...iew-round-up/7
It seems the PSU is also made by Seasonic!
However one quirk of the Asus motherboard is that you need to use a switch card if you are only running one graphics card.