Anything below 75 C, is good. Some can go up to 80-90 C, but thermal breakdown occurs around 135 C, but it depends on the chip. AMD are a little hotter then Intel, because of the manufacturing process.
The coolest thing about the newer (last 2 years) cpus, both Intel and AMD are that the have shutdown temperature built into the chip. The motherboard reads the temp and when the cpu is getting close to unsafe temps, it shuts itself down.
That's a pretty cool feature.
I fact my mother cpu fan broken and wasn't spinning. The computer would shutdown, and the cpu saved itself. Put in a new fan and away we go.
Soyo Dragon Ultra Platinum Edition powered by a P4 3.06GHz w/HT @ 533FSB
ATI Radeon X800Pro 256DDR <---Yeah!!! I finally got it!!!
1024MB PC3200, Creative Audigy LS, 2 x 40GB = 80GB RAID 0
Windows XP Pro, DOOM 3, CS, UT2004, BF1942 RtoR, CNC Generals
Finished Half-Life 2!!!!!!!!!!