New heatsing/cooling

I have AMD Athlon 64 3000+ Winchester 1GHz FSB Socket 939 processor. Can anyone suggest me a new not too expensive cooling system for it? Cause it runs at about 55 degrees all the time.

Try to clean up your case wiring and get rid of the dust in your case before you upgrade your cooling. Take the temps inside your case and see if it's your case or CPU that needs cooling.

I use a thermalright XP-120 with a 120mm fan and I wouldn't recommend it to anyone for a long term approach to cooling K8 processors.

This is mostly because of it's size. Mine is in place mainly because I will be moving toward phase-change cooling in the coming months. However, the size of the heatsink limits my choices on memory. I'm stuck at 1Gig until I change cooling-devices. This is also mainly because I'm sticking with extremely low-latency memory. With that said, the max memory of this system will probably stay at 2Gigs total. That is unless matched pairs of 1GB chips come out with latencies of 2-2-2-5 or lower. Then I would migrate to a max of 4Gigs (architecture limited). However, the possibility of that is mostly non-existent. DDR2 seems to be a trend-leader at the moment.

Back on track - I have to agree with TomK. First, check the airflow in the system and also ambient temperature of the room. Putting the system into a cooler part of the room, or even changing the fans to higher CFM ones may benefit better.

Most of the K8 coolers you will see are humongous. Unless a new breakthrough is made, small footprint coolers will not offer the cooling abilities to drop those temps too much.