Just my pint into the fire:
X2 4200+EE & GF6150 board (MSI K9NGM2-FID)
$240 (170+75)
E6300 $ G965 board (ASUS P5B-VM)
$285 (185+100)
Conclusion:
Anything cheaper is K8 vs. Netburst so Intel is no contender.
Anything more expensive is K8 vs. C2D clock/clock so AMD is no contender (4800+65nm is more expensive than E6400 it matches by perf.)
For decent IGP-free boards the difference is comparable.
So, going for
stock performance the choice is simple:
<$300 for CPU+MB combo go AMD X2
>$300 for CPU+MB combo go Intel C2D
for overclocking:
<$240 for CPU+MB combo go AMD X2
$240-$285 -> wait and then Intel C2D
>$285 for CPU+MB combo go Intel C2D
for power consumption (i.e. PC's for office use):
AMD X2 3800+EE to 5000+EE (anything above or down is a waste of money in this case)
for single core:
<$190 for CPU + MB combo -> go AMD A64
$190-$230 for CPU + MB combo -> go AMD X2 at $240
>$240 see dual-core recommendations
That IMO sums up the whole Desktop PC market as of now.