what will be the next way to cool a processor

Try bigger fans with higher RPM and a better case that can handle air flow efficiently. If that doesn't work, then I would say try liquid cooling. Its a bit on the expensive side but it works quite well. Nitrogen should only be used on extremely high overclocked systems.

Two of the most efficient ways, without using water cooling is to get a passive (no power needed except the heat itself) heatpipe type of heat sink combo (Thermaltake TMG i2 CPU Cooler For Intel LGA775 or Thermaltake Big Typhoon 4 in 1 Heatpipes CPU Fan) or a Peltier effect electronic cooler (which is electric powered).

fans should only be used as a backup cooling system with the modern pc's. Personally, i have just removed one side of my pc case to keep it cool, although my pc is only dual core and not quad core. Water cooling and something called Artic Ice are good cooling methods, although a desk fan pointed at your pc should be ok. I also reccomend a free program called Everest Home Edition to keep an eye on operating temperatures of all pc main components including cpu, gpu, mem and mobo