Wow nice to see people still using the P4. The should be a LGA 775 chipset, I'm still using stock heatsink and it runs quiet so I never bothered looking for an aftermarket cpu heatsink. Lucky for you.. that's supported in majority of heatsinks. The usual favorite is:
Make sure you measure before you buy. My motherboard is a little higher than most and some of the bigger 120mm heatsinks don't fit. Measurements should be provided. I recently bought the following model and it works well on an i5-2500K: