Im going to be completly re-building my PC soon, everything except the case and GPU is being replaced. Not usre what to get though

These are the current specs:
Asus A8N-SLi Deluxe (Socket 939)
AMD X2 3800+ OC'd @2.5Ghz
1Gb PC3200 DDR RAM
160Gb 7200RPM Maxtor HDD
BFG OC'd nVidia 640Mb 8800GTS GPU
550W PSU
Thinking on upgrading to this:
Asus P5N-E SLi (Don't need SLi, any better boards for the money?) -
http://www.komplett.co.uk/k/ki.asp?sku=329410
Intel Core 2 Quad Q6600 (after 22nd, how much will these be in the UK?) -
http://www.komplett.co.uk/k/ki.asp?sku=330169
Corsair TWIN2X 6400 DDR2 2048Mb -
http://www.komplett.co.uk/k/ki.aspx?sku=312054
Seagate Barracuda 7200.10 500GB SATA2 16MB 7200RPM -
http://www.komplett.co.uk/k/ki.aspx?sku=320711
Not sure on a PSU yet, need on that will cover all this fine, and be suitable for some CPU OC'ing
Please offer suggestion / improvements. My budget is around