Pbartender
First Post
I use PBworks PBWiki, which has its foibles but does the job really well.
Editing pages is just like using a simple word processor; you can upload images and easily link them into your articles (or just link to an external URL). You can organise your pages into folders, determine permissions for your players... all standard stuff for a wiki.
I've used PBWiki in the past, and liked it.
The big problem I had was getting and keeping the players involved with the wiki... In general it'd end up with me doing all the work to edit it, and me being the only one who bothered to read it.