I use a Forge 007p recirc valve, but it's anything but quiet. When it was on my mates S3 it was super quiet and he was looking to replace it with a splitter valve for more of the chav noise.
I think the noise produced has a lot to do with the surrounding pipe work. For instance on my car all the intercooler pipes are metal, and it has a large cone air filter. The noise on the S3 was a lot more muted beause of the connecting rubber hoses. It's simply the sound of air being dumped into metal pipes and through an open air filter.
If you want really quiet I could suggest something like the plastic bosch valves used as standard on things like 996 turbo's. It's used on loads of cars, but I can't remember the exact model number.
I've tried a lot of valves from cheap ebay knock-offs to good quality recirc valves, including:
HKS SSQV: wayyyy to loud, past the point of embarrasing and quite literally ear piercing.
Bailey BOV: Again, very loud and draws far too much attention for my liking.
Bosch plastic recirc valve: Quietest of the bunch but it'd always be in the back of my mind it was leaking boost.
Forge 007p: Best of the bunch. Quite a bit louder than the plastic Bosch valve but nowhere near ridiculous like the BOV's. Servicable and Forge provide great support including free service kits etc.
Thats my 2p.
