I second Noctua.
http://www.quietpcusa.com/search.aspx?SearchIn=0&Type=1&Keywords=Noctua&SearchField=1&selLimit=50
http://www.quietpcusa.com/Noctua-NF-P12-Vortex-Control-120mm-Quiet-Computer-Fan--P377C0.aspx
http://www.quietpcusa.com/search.aspx?SearchIn=0&Type=1&Keywords=Noctua&SearchField=1&selLimit=50
http://www.quietpcusa.com/Noctua-NF-P12-Vortex-Control-120mm-Quiet-Computer-Fan--P377C0.aspx