Ever heard about Dell's Ideastorm? While lots of features and new products have been implemented thanks to this submission and voting system, Ideastorm itself is probably the most significant concept to emerge from that brilliant spark of inspiration. With it, Dell gained a lot of points in the eyes of many by proving that they really do listen to their customers.
Whether or not inspired by Ideastorm, Google has recognized the value of a community-driven brainstorm, and has their own set up in the form of Google Product Ideas. Sure, the name is drab, but their collective heart is in the right place. You can read a bit about the project over at the Google Mobile Blog.
Go ahead and submit your own ideas or vote on those of others at Google Product Ideas.
I have quite a few, but my first suggestion is a Google Product Ideas Android app!