I've blogged about several companies in this space before - Fabjectory, JuJups, and FigurePrints among others - but in some ways Fabidoo seems the most likely to succeed. First of all, they've got their pricing in a range - $15-$50 - that supports an impulse buy. Second, their toys seem to be designed for the cell-phone hanger, back-pack hanger space that's quite popular.
Right now, their site is available only in German, so I had to struggle with a Google translation, but they seem to have a pretty good marketing plan. Technically, they are cutting no new path - judging from the photo, they are using a ZCorp 450.
This is still very early days for this business model, and you can be sure most will fail or at least fade away, but as the tools for 3D printing get more robust and less expensive it will continue to develop.