Hi. I actually use a Lga 775 platform and in the cover of the case it's attached one 140mm FAN from Akasa, with blue LED. It's good, but very noisy. What's the best solution in cost and benefits for me, please? I thought about Noctua. Ah! I also want to know a great CPU cooler with copper base and very tiny, since I don't want an enourmous big fan that can "crash" some sectors or the whole mainboard, please?
You might be going about this backwards, since I assume you don't have a power hungry video card or else it would have been mentioned.
Without a power hungry video card it is unlikely that you need a "cover of the case" fan at all, just the PSU's own fan and a very low RPM rear exhaust fan, and possibly to block that "cover of the case" fan mount so air follows the most optimal path, depending on where it's located.
However, your CPU heatsink should be large, so it is thermally efficient, and so a large-ish (12cm) diameter fan can be put on, so that it can spin at substantially lower RPM to result in less noise.
What is "crash some sectors or the whole mainboard"? It could merely be a 2" thick heatpipe tower sink with a ~1200RPM (max, controlled by motherboard fan circuit) 12cm fan on it, unless you case is too small for that.
If your case is too small or you have as much or more heat coming from the video card as the CPU, then you have left out some very significant info.