Back in 2008, The Lego Group started what is today known as Lego Ideas. This is a site where you can post a picture of a creation you've built and if your creation gets 10,000 votes, a panel of reviewers will look at it to consider it for production. There have been 9 sets released so far with one more on it's way sometime in 2015.
Take a look and see what's out there. The site is here. You can see some of the creations up for review next, vote on creations if you think they are worthy, and add your own creations to the site. Be sure to read the guidelines before submitting.
Happy building!