The sound of the SM57 defined the tone of the electric guitar throughout the classic rock era. Countless archetypal riffs by artists like Aerosmith, Eric Clapton and Lynyrd Skynyrd were recorded by placing a SM57 right against the cloth of the guitar grille (often a blackface Fender Deluxe Reverb or Fender Champ). Today, the inexpensive "57" still reigns superior to microphones costing several times as much and can be found in virtually every recording studio.
A contemporary favorite, the Sennheiser 421 captures a warmer, yet darker tone than the SM57. It features a rotating dial that alters frequency response, granting the engineer a variety of tones at his fingertips. Use this as an alternate to an SM57.
The KSM32 condenser microphone sees more action on guitar cabinets, especially in live settings. The tone is darker than the aforementioned counterparts, and this rugged mic's outstanding frequency response (greater than both the 57 and 421) make it an outstanding choice. The price point of the KSM32 towers over the 57, and is about $200 more than the 421.
The Royer-121 created waves with its 1998 release as a rugged ribbon mic able to withstand high sound pressure levels (SPLs). Before the 121, ribbon mics were considered fragile and could break in excessively loud conditions. The 121 and the newer 122 allow the robust sound of a ribbon mic to work on the loudest of electric guitars and have become staples for world-class engineers such as Bruce Sweiden and Eddie Kramer.