Amazon.com: CISCO Headset 561, Wireless Single On-Ear Digital Enhanced Cordless Telecommunications Headset with Standard Base for US & Canada, Charcoal, 1-Year Limited Liability Warranty (CP-HS-WL-561-S-US=) : Electronics
Clear-Com CC-300-X4 Single-Ear Standard Headset | PSSL ProSound and Stage Lighting
Standardized Headset Identification System | Park Tool
MEROCA Mountain Bike Headset 44 MTB Ultra-light Standard Headset Sealed Bearing | eBay
The ultimate guide to headsets - BikeRadar
Dan's bike stuff: Headsets and associated standards