cclonline.com is the best site I've used, and I've used most. The 4800 is a tough CPU to find and it's holding the price on both retailer sites, (where found), and eBay, I think it's due to over estimating the 2-3% performance the 1mb L2 gives you over 512kb models thus making it considered the best CPU for 939s. Get a bargain off eBay, and don't forget that Opterons fit 939s, (I assume you have a 939 and not AM2 or you'd be looking for a 6000+), 165-180 are all DualCore, and they overclock a little better.
Can I just add www.overclockers.co.uk are way too overpriced, they had pre-ordered X1800XTs at about £370, cclonline had mine sent on the release week for £305, although it may have been luck.
Yeah it's a socket 939 my pc is now 3 and a bit years old.. Not bad really it still plays most new games but the 3200+ is definitely bottlenecking my 7800GS. I had assumed the opterons were not as fast as the Athlon x2's was that wrong??