A channel strip is a device that allows the output of an audio device to be amplified to a line level and integrated into some other system. An audio channel strip may be a stand-alone unit or one of many units built into a mixing desk. It usually includes a microphone preamp with a switchable phantom power voltage to power condenser microphones and some form of audio equalization.
Some designs also offer other facilities including audio compression, de-essing, noise-gating and limiting.
Some popular brands to take a look at would be - Neve, Rupert Neve Designs, API, Drawmer, SPL, BAE