I would love to see the ability to create a navigation menu that stays visible and has custom links. My main wiki page is quite long and I currently have a menu written in html added to the bottom and locked in place in the upper left corner using CSS. The main advantage for me of having a menu like this is that I can link to anchor tags in my main wiki page to jump around inside it as well as link to external pages (where we store xp). Currently I have to copy this html across any pages that I'd like to see it on, but I can't include it on the adventure log/character list pages since I don't control what's shown there.
An example of what I'd like is "here":http://www.obsidianportal.com/campaign/crimsonknave-s-test-campaign/wikis/main-page