I can second the Gigabyte boards, they are really fast and also reliable, just got one myself and it's great.
Two things with psu, the most important being efficiency, the second wattage. An efficiency in the high 80% is good, and a lower wattage with higher efficiency can sometimes beat high wattage with lower efficiency. Efficiency isn't being measured by all manufacturers yet, but the good ones are.
£800 will get you a stonker of a pc if you diy, I put one together for about £600 that I'm really happy with, including 19" widescreen monitor (lcd) which I got from dabs for 110 quid, and an Audio Kontrol 1 usb soundcard.
Happy building, and don't forget to earth yourself :)
oh and get a good psu, it meant the difference between the soundcard working or not for me.