I really like UseModWiki - http://www.usemod.com/

The first time I installed it, I probably spent a little bit of time getting it running, but since then I've dropped it on Windows, Linux, and Mac OS X boxes, and had it up and running in a matter of minutes.

It might not be as full featured as the others (then again, it might be and I didn't notice or care) but it does what I need it to do.