MadShrimps has posted a brief article which outlines a budget-oriented mission to overclock two different Intel CPU's well beyond 4GHz. Both the moderately priced Pentium D 805 and the Celeron D 356 were placed in an ASUS P5LD2 motherboard and cooled by a Thermaltake Sonic Tower heatsink. Seeing 4GHz in the rear-view mirror using standard air-cooling is certainly an accomplishment. The fact that it was done for such little money is nothing short of impressive.
The price of this CPU (Pentium D 805) is extremely low which makes it a winner as a budget CPU, even when not considering overclocking, a Dual Core CPU at this price is the best thing Intel has done up until now this year! They've also included a better standard Heatsink/Fan combo which supports auto fan speed adjustment, allowing the Fan to be quite silent when running idle. For the price this D 805 runs almost as fast as the best out there when overclocked.
The draws backs are its high power consumption and when overclocking you'll have to invest in better cooling to keep the temperatures down. The Asus P5LD2 limits the overclocks to ~200FSB, going any higher you loose the SATA ports.