3D files ready to print:
Yeggi – Search engine for 3D printable files. Searches multiple other major sites.
Thingiverse – Database of 3D printable files, owned and run by Makerbot.
BLD3R – 3D printing social networking site and searchable model database for 3D models.
Cubehero – 3D printing website.
My Mini Factory – 3D printing website.
3D file design:
Tinkercad – For beginner to intermediate designers. Free (requires registration).
Blender – For intermediate to advanced designers. Free and open source.
Arduino – Open-source electronic prototyping platform allowing you to create interactive electronic objects.
Cubelets – Inspiring the love of learning through simple robotics
Makey Makey – An invention kit to turn everyday objects into touchpads and combine them with the internet.
Raspberry Pi – A low cost, credit-card sized computer that plugs into a computer monitor or TV, and uses a standard keyboard and mouse. It is a capable little device that enables people of all ages to explore computing, and to learn how to program in languages like Scratch and Python.