Sony ECM 55/ ECM 50 by John Eppstein
You've seen this mic clipped to the lapels of newscasters and media personalities all over TV. It's a broadcasting staple, as well as a common mic for actors in musical comedy stage production.
BUT IT DOES SO MUCH MORE!
The small size of the mic head and smooth, wide response make it a secret weapon in the studio and live sound reinforcement. My favorite us is for amplifying acoustic guitar - clip this mic inside the sound hole and you minimize leakage from a singing guitarist's voice, leading to vastly reduced phasing issues. In addition you don't need to worry about the musician moving around relative to the mic. It's an omni so there's no proximity effect and it gives a surprisingly natural tone - much, much better than the piezo pickups built into many instruments. This mic can also give a good sound on upright piano - just drop a pair of them down inside and close the lid on the cables to hold them in place. Hang one inside the lip of a gong unlike most mics it won't get in the way. I've had interesting results taping one inside a djembe (experimentation with placement is crucial), and they've been used on acoustic stringed instruments such as fiddle, especially with a player who moves a lot as many fiddlers will do.
Current version is ECM-55B. ECM-55 replaced the ECM-50, the primary difference being that the battery for the 50 is unobtainium. This doesn't matter in a studio setting, as the mic also accepts phantom power. I own one 50 and one 55.
Comes in a metal box with tie clip mount, windscreen and battery. Format is miniature microphone head with a long, thin cable attaching it to the preamp body. Studio quality omnidirectional electret condenser.
Can often be found used at an EXTREMELY reasonable price.