Cooler Master has announced a series of "Silent Coolers". With options for Athlons, Celerons, Pentiums and most other chips, this line seems to be fairly comprehensive.
Details are sparse on the site, but the HSFs appear to be nothing more than a big heatsink with a large fan stuck on top of them. Some of the "Silent Coolers" have noise ratings as low as 26dB(A) while others range up to a migraine-inducing 38dB(A). It remains to be seen how Cooler Master intends to distinguish these HSFs from the rest of the very crowded field.