Has to be the Q6600. Made Quad core computing affordable with great performace to boot, moreover it clocks like hell 
Have a good old Celeron 333 as well which is a good chip, used that at one point for my retro rig that had 2xVoodoo 2 8MBs in SLI and a Rendition Verité V2200 4MB for the ultimate oldskool gaming experience

Have a good old Celeron 333 as well which is a good chip, used that at one point for my retro rig that had 2xVoodoo 2 8MBs in SLI and a Rendition Verité V2200 4MB for the ultimate oldskool gaming experience




I was running it at 1.2v for a while and the stock volts were 1.325, and considering I was running it a hell of a lot faster than stock, I was very impressed with the chip.