Here's another 140mm fan roundup in googlenglish
be quiet SilentWings 2 , Bitfenix Spectre Pro , Cougar Vortex HDB , Deep Cool UF 140 , Silenx Effizio and Thermalright TY-150 are recommended.
I've heard good things about be quiet Silentwings, but I'll probably replace my 120mm Scythe S-flex with a TY-150. They are very quiet, move a lot of air, start at under 5V, scale from 500rpm - 1200rpm and have a high quality motor (Sanyo, I believe) and high quality bearings (double ball bearings, potentially not as quiet as fluid bearings but apparently better for longevity).
They have unusual mounting holes in a 105mm X 125mm pattern (120mm fans have 105mm hole pattern, 140mm fans have 125mm pattern, I think).