If anyone knows... who makes the OEM Navigations for MB?

THe majority harman becker. There's a couple that use alpine.

Thanks, would you know which of these would be in after market double din decks? I'm looking for something extremely similar to what is in my C55

What do you want it to do?

PS- it is irrelevant who makes the system for your C55.. they all operate pretty much the same way.

ex. I have an SLK that has factory Alpine HU, Alpine Cd changer, Bose amps and speakers.. and an S500 that has Factory COMAND navigation (which i'm pretty sure says Bosch on the back of it), and an Alpine changer, bose amps and speakers.

Your C55, if it has COMAND Navi, will lose the steering wheel controls and some other functions if you take it out. You will also have to bypass the factory amps if you want it to work because the HU and the amp on the COMAND units use a fiber optical link. If you want navi, and DVD/Mp3/CD/TV tuning/Aux audio and video inputs, just get a european Comand unit for your Benz. They are multi-regional, and the Radio Tuner that's already in your car's trunk somewhere will determine what region setting it will use. In plain english, it'll work perfectly, and you'll get to keep your steering wheel controls and every other function.

If my SLK had COMAND like the S500, I would not have bought my avic... I would've just gotten the euro version.

You should check out http://www.mbenznl.com/index.php for COMAND and other MB stuff. I bought a Euro version of the COMAND for my wifes C class from them and they were great to deal with.