Tom Coates wrote a piece I somehow missed back in August, about building a not-ugly wiki for their intranet at the BBC, and some of his research on which bits of which wikis worked best:

Anyway, over the last few weeks the team that Matt and I work with has been trying to put together a wiki for our intranet. I think they've demonstrated that maybe there are ways of keeping both camps content - simple, adaptable Wiki designs can be made that are also elegant and attractive. First things first - here's a quick thumbnail of Kate Rogers' design ...