Not an easy answer. Let me give you some things to look for in a board for each category...then you can find one that suits your specific needs.
-corporate server-
this one really depends on what you're running. if you're using unix...well then I hope you're already hardware savvy enough to know. but if you're doing something on a much lower scale, as in Win2k Server, then I would recommend looking for a board with more than the default 2 ide channels. I think you can actually find some reasonably priced boards with 4 ide channels (that's 8 ide devices!). this is not an issue if you are going to be using scsi devices. other than that...it's all bells and whistles really. you want something that will use around a gig of ram and has a few security features -- ie., chasis intrusion, heat monitors, etc. Some of the other nice features to look into are wake on lan, wake on ring, and built in networking hardware.
-graphics-
hands down, you need to have a board with an agp pro slot. granted, the pro boards are E X P E N S I V E...but you're a designer, right? so no problem. you have to have it. other than that, you want a board that will support a good deal of ram.
-gaming-
this is probably the most flexible niche, as it is the most heavily marketed. do your homework til you find a board you like.
-word processing-
if it supports a processor, you can run office applications. this is the simplest category as word processing does not require very much power.
