Is there a camera out there (dSLR-class) that offer's a one-touch (or nearly) ability to view a shot in black and white? Also, what about LiveView functionality with realtime black and white?
Realtime B&W is available on all SLDs and SLRs with Live-View.
It is also available on the Fuji X100 which is a (almost) compact camera with a sensor the same size (APS-C) as most DSLRs. Probably does not count as SLR-class unless you only consider the image quality.
Many entry-level DSLRs and even some pro ones now have in-camera effects or conversions which can convert to B&W. It is far from one-touch though, requiring 5 to 10 button presses.
Recent Nikon DSLRs like the D90 and D7000 that have Picture Controls, have a monochrome setting which will display B&W on the LCD. If you shoot RAW you can override the picture control in post processing and still have a color image if you like. JPGs would be produced in B&W.
I believe Live View will also display according to the picture control, so would display in monochrome. I will have to try it and confirm.
They also have in-camera image editing, which you could access with a couple of touches if you set them up in a custom menu.