Via the Antec NSK-3480 (90 euro) on the best silent cases list (http://www.silentpcreview.com/article763-page1.html) I found the NSK 4482 - EC (92 euro) which has a better PSU (80 Bronze) and isn't limited to uATX motherboard sizes. On Newegg they say the EarthWatts 380D Green is (very) quiet.
Edit: Yesterday I read several (user)reviews and the overall feeling about these cases dropped cause of some disadvantages pointed out. Therefore I reconsidered the Cooler Master Sileo 500 and saw it has dropped in price since the introduction of the Silencio 550. The Sileo can be bought for 60 euro and the PSU (a be Quiet 300w) for 35 euro.
Looking at the review on this site, I think the Sileo 500 is the best buy for this budget. Don't you think? Other ideas are always welcome
![Wink ;)](./images/smilies/icon_wink.gif)
FYI: It will be housing an Intel i3/i5 Sandy Bridge IGP system.