More open source 3D printing models than you can shake a 3D printed stick at. They're all about making, sharing and discovering. They have over 100,000 3D models. This has got to be just about everyones 3d printing resource of choice.
But don't get stuck printing other peoples models, learn how to design your own 3D models in the 3D Printing Software section. Then you can share back to the community too.
So, I really like MakerFarm as you can probably tell by now. But, I am not affiliated with MakerFarm other than being a very happy customer. Their kits come with access to a PDF build instructions and each major step has a YouTube Video showing how the parts are put together. And, for the few questions I had to contact them, they got back to me right away.
Plus, they have all kinds of parts and upgrades for your kit or for other RepRap based 3d printers.
Ebay has a huge 3d printing resource. Tons of items for sale. Beware of super cheap filament since the diameter can vary and cheap ABS filament apparently stinks a lot more.