AMD offers great value, and is generally preferred for most gaming builds under $1000.
Intel currently owns the high-end of the processor market, as their i7 series has hyperthreading, which lets each physical core appear as two, allowing more work to get done when the cores aren't maxxed out. Hyperthreading is useful for audio editing, 3D rendering, video editing, etc. (processor intensive tasks), but it isn't used in gaming.
My general recommendation for gaming builds is:
Under $1000 - AMD Athlon II X3 or Phenom II X4
$1000-1500 - AMD Phenom II X4 or Intel i5-750
$1500-2000 - same, plus start to consider Intel i7-930
$2000+ - whatever you want
For workstation builds that won't be gaming, you can consider the AMD 1090T in the $1000-1500 range, as well as start considering the i7 there, as there's usually no need for an expensive graphics card.