Well I'm not too familiar with allot of the sites mentioned on this thread, but if you are only planning to use a wiki-based site for your own role playing group/campaign, then you might want to consider the Obsidian Portal which is a nice Textile based wiki site that offers a limited range of HTML and CSS formatting as well. There are both free and paid accounts, the latter offering a few extra options and tons more data usage. I've personally used the OP to record notes for two different campaigns, as well as to construct my own campaign setting (if you are interested it's called Age of Legends). Don't know if this is what you are after or not, but it may be worth checking out.

Cheers,
-Arsheesh