For the budget end, the Pentium D 820 and 805 completely crush the X2 3800+ in terms of price vs. performance. The price difference between the 820 and the X2 3800+ is quite large, however the performance difference is very small usually.
Also, it is not wise to listen to AMD fanboys(nor Intel fanboys for that matter). The X2s do not completely destroy Pentium Ds in any case. They are competitive with each other in just about every case. There is no app you can run with an X2 4800+ and Pentium 840EE that you can tell the difference between them in. Granted, there are times when the X2s do pull further ahead, what people fail to mention however, is that there are also times when the Pentium Ds pull ahead. In Photoshop, a Pentium D 820 is faster than an X2 4800+ by quite a margin.
For pure gaming purposes, you have no reason to buy a dual core in the first place. For general use and lots of multi tasking, as well as the occasional game, the Pentium Ds and X2s are competitive with each other with the nod going to the X2s. However, if you are on a budget, and use your pc for lots of things ranging from encoding to gaming to heavy multitasking, Intel now has the crown. The Pentium D 805 very commonly overclocks to beyond 3.5Ghz on moderate air cooling. If you want to get even more into it, one could say without argument that the entire Pentium D series overclocks better than the X2s.
I am tired of people with their blind faith to individual companies. When one company offers a better product for the price, one should go for it. Only a fool would stay beside one company regardless of how much better the others product may be.
The enthusiasts in this forum, as well as many others, are largely responsible for the high prices from AMD processors. When the Athlon XP 1800+ launched, it was AMD's top of the line processor. It was faster than the Pentium 4 2Ghz(Intel's Flagship) in just about every test. The Athlon XP 1800+ had a price of under $300. Nowadays, to get AMD's top, you need to spend over $1000 for it. Why you ask? The answer is that all of the fanboys will suck it up and pay for it rather than finding an alternative, and AMD has taken advantage of this fact.
Competition drives prices down, blind fanboyism pushes prices higher.
\Rant.