Intel Core 2 Quad 9400 2.66Ghz
This was a tough call. When AMD released the X4 940 and 920, it seemed clear that AMD's processors provided a better value than anything in Intel's Core 2 Quad line-up. Intel responded quickly, however, slashing prices across the Core 2 Quad line by significant amounts. Once upon a time, the Core 2 Quad 9400 was a mid-$300 dollar processor. But now it is only $229.99.
As a result, the Core 2 Quad 9400 gets a nod. It is a nod that comes with a few reservations, the largest being that the value in the processor comes exclusively from its placement in the market, and not from any interesting features, like the X3 720's unlocked multiplier. If you are looking at processors under $200 dollars, it is very likely that you can't make a better choice than a Phenom II.
On the other hand, an extra $60 lands you a Core i7 - which nudges out any of the Core 2 Quads. But you also have to factor in the extra costs of the X58 Platform. As a result, the Q9400 wins nearly by default, as it fells all contenders in this price range, including AMD's new quad-core Phenom IIs, which are competitive but not-just-quite good enough to dislodge an Intel recommendation.
Overall, this may seem a negative recommendation - so allow me to lighten the tone. If you're looking for a quad right now, and you want to keep your budget as close to $200 dollars as possible, you should blow the extra $30 and buy this one, without a doubt. The cheaper quad-cores, from both Intel and AMD, are starved for speed. They are too slow for intensive applications that don't make good use of multiple threads (gamers, I'm looking at you).