Quiet Components/Configurations Phrased towards someone looking to purchase a new commuter bike, I prioritize a quiet smooth ride when possible.  One of my past issues is that bikes are often great on the test ride but pretty quickly develop a lot of "personality."  Are there some recommendations as to which components or brands are the quietest without too much sacrifice of functionality?

(Note: No, I am not planning illicit bike-behavior!)  

Gearing:  I expect a fixed gear would win by far, but that's not really my interest. Other than that, will fewer gears produce best results?  

Hub:  My old Raleigh freewheel actually had a beautifully quiet ratchet (softer than most cassettes I hear), but it took me a while to find one that doesn't start clicking after a few rides.  Is there a type/brand of cassettes which will do better? 

Shifters:  I've been using downtube shifters which are great- no "click click THUNK".  But if they don't line up just right (user error) they can be a loud bother.  

Tires:  Best results I've found are totally smooth tires.  Does width/pressure affect this much?

Brakes:  I've not had a bike with anything but hub brakes.  

Accessories:  Racks are out.  Fenders are iffy, but removable is best, noise doesn't matter much in the rain!  Of course an item to make noise for when I need it :).
An internally geared system would be the quietest option available for a commuter set up. A groupset such as Rohloff, Shimano Alfine or SRAM would offer near silent operation. You could pair this with a belt drive train to reduce this further. This would also alleviate hub noise. The Rohloff probably has the quietest shifter as it is not indexed.

For brakes I'm not sure if there is any difference between the noise made by rim vs. disc brakes although when they bite they may be louder than a coaster brake but much safer. Disc brakes would be my recommendation if your were considering cycling in the rain. There is no difference in noise between mechanical and hydraulic set ups but for commuting 140mm mechnicals would be just as effective as hydraulic brakes (unless your doing technical descents) as there would be very little differentiation in modulation and they are easier to maintain.

Accessories will be all about what you choose, how you fit them and how you maintain the bike. You will need to keep things well lubricated to keep noise down (anything with a bearing) and taking time to fit things properly and to the right torques (such as bottom bracket). Pumps and tools can be placed in old tubes to keep them from rattling.

For tires I dont think totally slick is the best option, also where you have said rain was an issue but something that had a specifically noise and puncture resistant tread and a low rolling resistence would be best for commuting.