Well first i tried the Delta fan:
4900rpm, 45dBa, 68.5cfm.
That was waay too loud. Next i tried a pabst fan:
3600rpm, 34dBa, 45cfm.
That wasnt bad, but still too loud.
Recently, when i got my shiney new aliminium case and overclockable cpu i tried a really low speed fan, The Panaflo:
2000rpm, 21dBa, 24cfm.
It is one SILENT fan!
Probably the best allrounder is the Smartfan2, as it varyies according to the temp of its probe. with the probe stuck to the copper block of my heatsink it usually varies from 2500 to 3500rpm. With quite decent noise levels.
Mind you, even the panaflo worked well with my XP1700+ overclocked to 1833Mhz @ 1.70v (25% OC)
<b><i>The Very Hungry Caterpillar</i> - George W. Bush's favorite childhood book.
Note: This book was first published a year after Mr Bush graduated from College.</b>