i have a 550 and the Asus P5GDC-V, so i know exactly what you're going through. my idle was 52c and load was 68c, which would cause the cpu to throttle. I of course replaced the stock fan right away, but those temperatures above were with a zalman cooler!!! overclocking was just out of the question.
Now it seems as though you have two options here...
1-watercooling (if you have a small case, this might be the only option)
2-GIANT heatsink
I went with number 2.
I got the Thermaltake Big Typhoon, which is a monster of a heatsink, but believe me when i tell you it works wonders. Idle is now 38c, load 49c. When i overclock from 3.4ghz to 3.68ghz, load temp goes up by 2c.
another thing to consider is your case's layout. a case with the power supply directly above the heatsink will NOT help, put your finger between the two and feel for yourself.
the other thing would be to get good case fans, i'm running 3 120mm fans, which can run quietly because they push more air per RPM.