Hi Hawky 89,
Had similar problems to yourself having just bought a e8400.
Using:
Tsunami Dream (Thermaltake) Case (2 x 120mm fans)
Asus P5N-D Motherboard
Installed it with the (suprising small) stock cooler and had conflicting readings. After trawling the forums most people seemed to agree the best monitoring device was Core Temp. My temperature references (below) are from this device.
http://www.alcpu.com/CoreTemp/
Anyway bottom line the temperature whichever device I used was too high for my liking. 45 to 46 celsius idle, up to 59 whilst gaming and over 60 celsius stressed (orthos).
My PC is in one corner of a room, not a great deal of ventilation behind and the room itself is always has the central heating on. I knew it wouldn't be possible to get the CPU really cool but over 60 celsius for me was unacceptable.
Trouble is with CPUs is no one really seems to know what a maximum safe operating temperature is or even if there is one. Cooler the better (within reason) to ensure the longevity is the only concensus of opinion.
Anyway I bought a Arctic Cooling Freezer 7 Pro CPU Cooler from overclockers and some Arctic Silver 5 Thermal Compound . When it arrived I couldn't believe the size of it compared to the stock cooler (3 times the size). Really easy to install.
Same tests now give 40 to 42 celsius idle, up to 49 whilst gaming and 50 to 51 when stressed with orthos. This for me is acceptable due to the conditions of the room and the fact I use only 2 case fans.
I might add my CPU isn't overclocked, if I did I think I would invest in water cooling.
So do yourself a favour, get a decent CPU cooler (not expensive) and like me I guess you will cleave 10 degrees off its maximum operating temperature. I'm happy with a maximum temperature when gaming of under 50 celsius.
Best of luck buddy. Norton.