You're not getting much in the way of suggestions so far so I'll try and start the ball rolling.
The Antec P183 Super is often quoted as the obvious candidate, although I have reservations.
Another is possibly the Antec Sonata III. I think it's modest in size and its been around a while.
Supposedly NZXT do some decent quiet cases although OCUK only stock the Full Tower versions - the giveaway is in the names they give to them.
I'm looking for a quiet case myself and am tempted towards the P183 although I'll probably go for the Lian-Li B25FB.
I'm not suggesting the Lian is necessarily quiet, although my current Lian is extremely quiet, but I like them and I have a feeling no matter what I buy it could well be louder than preferred, so I could end buying some replacement fans and/or use a fan controller.
Obviously what you put in it has a major effect and whilst a quiet case seems like a good place to start, it may not be the major factor unless you give a lot of thought and priority to quiet components.
The other issue is that some of the quieter components ie GPU's aren't necessarily the most capable or best value for money.
So dependent upon how important noise is to you, it may end up compromising you elsewhere ie performance and cost, in order to keep the noise down.
If I come across anything more promising in the next few hours or days before I buy I'll take the liberty of posting.
Not sure if that helps at all so consider it a bump.