I have the Distagon 4/50 FLE, Planar 2,8/80 and Sonnar 4/150 CF lenses, and honestly, I have no complaints about any of them! I use them on a 503CW. They're more plentiful and cheaper than the 60/100/180 lenses, which are supposedly "better." Can't say, personally. Though my experience is limited to CF lenses and not the newer ones (basically the same optical formula in most cases, just updated w/electronics for later bodies). You can use them on the 200 series cameras by just not using the internal leaf shutter... Though the FE lenses are generally a stop faster on anything other than the 80mm.
With digital backs, you really have to keep the crop factor in mind - as wides aren't nearly as wide as with film. In my case (CFV16) there's a 1.5x crop. The CFV39 is better, depending. Using the full sensor there's a "1:1" crop, but only along one axis. A bit misleading. Using the square format mode, you're right at 1.5x again. So a 50mm lens isn't all *that* wide...
There aren't many lenses that are wider - the most common is the 40mm. Because of this, the prices on these are astronomical as compared to the 50mm. The only wider lens is the 30mm - and that's a fisheye.
So my suggestions might include the Distagon 50 FLE and Sonnar 180.
Here's what the gang looks like: