If you want something with a lower clutter factor, try PC104 platforms--mini computers. The outputs are the same as a fullsize, and the form factor is stackable...you want another DAC board? Just stack it on. You can even get 640x480 flip down eyeglass monitors with twiddle keyboard and mouse, so you can look like the Borg driving through DV.
More realistically, you can stick the PC104 somewhere in your dash, or behind a body panel, or in the glove box, with a couple drives (DVD+RW, floppy, USB) sealed in a box if you need to connect them and connectors for drives, KB and mouse hidden under the dash. The CPU and bus can be hidden away wherever you want. All these small form factor units can run completely headless...boot and go. You can attach touch screens, regular monitors, LCD screens, whatever you like. A KVM-like switch lets you swap between cameras, nav units and computers. All you need exposed is the screen, the keyboard and mouse can hide until they're necessary. With a touch screen, you don't even need the KB and mouse...location + pressure = mouse click. Of course, you'll need to be a decent programmer to work that out.
There used to be a PC104 unit manufactured specifically to replace the stock HU, but I don't know what happened to it. Sometimes they show up on Ebay.
The downside to this sort of setup is that the computer becomes part of the truck...you can't take it in to the restaurant or next to the fire in camp.
-Sean