Making Wikipedia profitable
The Wikimedia Foundation is a nonprofit organization, so "Making Wikipedia Profitable" should be interpreted as "Making the Wikimedia Foundation a successful self-sustaining longterm nonprofit organization." Strictly speaking, monetary profit is not the objective, but at the same time a flourishing and successful organization needs to appropriately balance income and expenses, weighed against the overall mission of the organization.
Tried, Tested and Tired Methods 
- Banner advertising -- by universal consensus, this would be entirely unacceptable
- Keyword advertising -- by nearly universal consensus, this would be significantly unacceptable
- Corporate sponsorship not involving direct advertising -- for example, imagine if Google gives us $100,000 in hardware, and we put a link on every page 'benefactors', and when you go to that wiki page, Google is listed along with a quote of why they are sponsoring MediaWiki
- Affiliate programming
- An endowment
Exciting new 21st Century Methods 
- branded merchandising - t-shirts are always popular amongst geeks, print up some of the most favourite and oddball pages and sell hundreds.
- micro-payment system - add a small donation button to the top and tail of each page.
- Wikipedia CD/DVD - wait a while, bring across the majority of the well authored and edited pages to CD/DVD and add in loads and loads of multimedia content; videos, music, pictures. Package it up, sell it for a reasonable price and watch the money roll in! This is probably one of the best ways for Wikipedia to make money in the long run, there are still billions of people without high-speed Internet access (or any at all) and the added advantage of multimedia would even make it a draw for those who can get to the website.
- On Special:Booksources add a explicit link to a commercial online bookstore (for example Amazon.com), which will pay Wikimedia some kickback (Amazon.de pays 5%). Users who want to can use this link to buy their books there and donate to Wikimedia and the same time. (Bookzilla.de is a similar project paying 5% to the Free Software Foundation.)
- Fork the wikipedia.com away from wikipedia.org, and use a template with text merchant links for pages that mention products (books, authors, musicians, games, electronics). Add a "Flag this" mechanism so that if more than N people flag a page, the ads disappear.
Just as money gained the word 'currency' to indicate the flow of money, we now need to go meta on information to look at the flow of information.
How about an Experts for Hire page? 
So-called expert sites like guru.com and exp.com get a cut from the micropayments (think paypal.com) charged by their "volunteer" subject-matter experts.
See N.Y. Times article by Lisa Guernsey, February 3, 2000 Suddenly, Everybody's an Expert on Everything: Sites Turn Questions and Answers Into a Free-for-All, but Sometimes the Facts Get Trampled for an unvarnished look at this idea.
See also under proposed project. Mobile Phones(cellphones) provide a micropayment gateway which could allow wikipedia to generate a lot of revenue from it's existing content. WikiMobile is content organized in a mobile friendly format, WikiMobile by default is offered free to all devices. However data traffic to the site can be white listed, partnering with carriers for a small monthly subscription fee. That would enable users to have "All you can eat" WikiMobile page access. Since Wiki pages are more relevant then random searches on Google this would only prove to be a valuable mobile tool on the go. I personally could get this presented to quite a few mobile carriers in my industry if such a solution was developed.
One other suggestions (perhaps similar to above) is "WikiRequest", whether through mobile or web users can pledge a certain amount of $$$ to Wikipedia to attract people to research and develop on a requested subject. Lots of ways this suggestion can be explored.