The Yate Loons and Scythes seem to be very popular in these forums.
I got some SilenX 120mm fans recently because they claim to move 72cfm at 19dba - although in practice they don't seem to move that much air. They are relatively quiet though their LED's are very weak compared to others.
All in all, I can't recommend them at their $25/ea retail price. Good thing I only paid $8 for mine!
Scythe S-Flex. I run two of the 1600 rpm models as intakes controlled by a Zalman FanMate to keep them around 1000rpms and they are very quiet. If you get the 1600rpm fan...it is a bit on the louder side. My full setup also includes the 3 Antec TriCools on low, 2 Scythe 1600rpm/controller intakes, and Scythe 800rpm for my CPU. Very quite, very cool setup IMHO.