I am looking to build a project that will take video input from several different cameras that have composite output. I am wondering if there are any micro controllers or shields out there that will allow the micro controller to accept composite input? Even if it only were to accept one input I can setup a system for switching cameras. I would prefer to stay away from the usb capture devices.
A Leopardboard 368 plus a LI-VI365 video input board (connected to its optional camera interface) allows you to do both composite video input and composite video output. As indicated by the links in the previous sentence, both boards are available from Mouser.
The Leopardboard has a 432 MHz ARM plus a video processing subsystem. It is open-source and well documented.
The bottom line is, most microcontrollers (particularly toy MCU's like Arduinos) are simply not capable of dealing with video in a useful way, especially if they're trying to do anything else at the same time. The sheer volume of data defeats them.
There are system on chip devices like the ASC88xx line from NXP that are purpose-built video encoder/decoders but apart from being able to deal with video in a meaningful way they're unlikely to meet your needs (a powerful ARM CPU with video peripherals, in a BGA package, is not for hobbyists working at the Arduino level).
I'd suggest you restate your question and explain exactly what it is that you're trying to achieve. What do you mean by "will take video input", for example; what are you going to do with the video once you've digitized it?