Dave ... yes it's logarithmic ... from wikipedia:

"A decibel is one tenth of a bel (B). Devised by engineers of the Bell Telephone Laboratory to quantify the reduction in audio level over a 1 mile (1.6 km) length of standard telephone cable, the bel was originally called the transmission unit or TU, but was renamed in 1923 or 1924 in honor of the Bell System's founder and telecommunications pioneer Alexander Graham Bell. In many situations, however, the bel proved inconveniently large, so the decibel has become more common. (It appears to be a happy coincidence that, to the human ear, one B in sound pressure level represents approximately twice-loudness, that is, 10 decibels or so.)"

So a 10dBa increase in sound is a doubling of sound. a 10dBA fan you wont hear. A 20dBA fan you will hear. A 30dBA fan you will not want to hear. you can see where this is going

scar~face ... to answer your original Q:

Here is a whole selection of lit fans. The coolermaster and thermaltake one's look like they offer the best airflow vs noise profile. The evercool aluminium framed 3 LED fan is defo the glitziest if you don't mind losing a little performance.