32 kHz
32 kHz is a sample rate chiefly used in longplay DAT recordings.
It's also used by the obscure dictaphone format NT, and is theoretically supported by all MP3 encoders and decoders, although I don't think I've ever seen a 32 kHz MP3 file in the wild.
Longplay DAT's sample rate and resolution are pretty obscure, supported by a few standards but seldom actually used in practice. However, they're more than sufficient for consumer entertainment. I for one can't hear anything above 16 kHz, and I doubt I'm the only one.
Sample rates: 8.363 kHz | 31.25 kHz | 32 kHz | 44.056 kHz | 44.1 kHz | 48 kHz