Pssssst. Want to know a secret? Some of the best inventions are completely obvious. That is, given a half dozen years or so. At the time they're conceived, however, most good, obvious ideas just seem dumb, dangerous, or uninteresting. They have to - otherwise they'd have been developed already.
Case in point: the blog permalink. If you've ever read a blog, you know what a permalink is. It's the link you click when looking at a story headline in an RSS reader like Google Reader.
If you run a blog, you definitely know what a permalink is. It's the link that a Google user follows when they search for a topic you've written about. It's what other authors link to in their own writing, thereby increasing your ranking in Google. If your blog is anything like mine, Google drives a lot of your traffic, and the permalink makes it all possible.
A permalink is nothing more than a fixed, unique identifier (URL) for online content. Blogging would have never caught on without it.
I recently ran across Tom Coates' excellent essay on the lowly permalink. He describes the time around 1999-2000 when permalinks didn't exist. If you ran a blog back then and wanted to write about someone else's blog post, you had to link to the other blog's home page. As the author you linked to continued to post, the content you had discussed in your own blog disappeared from the other author's front page, making your link irrelevant.
It was a huge problem, yet few perceived it as such. Interestingly, Coates even admits to having been against the idea of permalinks because of their hacky nature. Besides, they didn't seem to do anything useful.
So the next time you're stumped while trying to find something to work on that matters, try picking up a dumb, dangerous, or uninteresting - yet obvious - idea and run with it. In six year's time your invention may become so well known that most people couldn't imagine the world without it.