3D models

Digimation's 3D Archive is a superb collection of over 16,000 high quality 3D models, available on multiple DVDs for $599. It comes with a browser that allows you to search for the models and sort them by poly count.

Archive3D features a huge number of 3D models in a wide range of categories, all freely downloadable. The quality is variable but it's an excellent source of free models.

NASA's 3D page offers a selection of models with a space theme. Some of the models are in native Blender format, so you'll need to download Blender in order to convert them to OBJ files.

3DM3  offers a small range of free-to-download models in19 different categories.

GrabCAD  is a resource mainly for CAD modelers, which offers a huge array of 3D models in a wide variety of formats. A good source of contemporary models, from iPhones to Ferraris.

Google 3D Warehouse is now officially known as Trimble 3D Warehouse Powered by Google , and is a repository of models mainly created in Sketchup (and Photoshop can import the Sketchup format). Best for architectural models, featuring just about every major building in the world.

Pond5  is a collection of mainly high-quality 3D models, available to buy from around $5.

3D textures

CG Textures is an extensive collection of textures specifically made for 3D modeling. Many of the textures are seamlessly tiled so they can be extended indefinitely. 

Mayang's Texture Library is a vast set of free-to-use images, not just for 3D work but for general Photoshop compositing as well. 

Useful places

HotChiPs Reader Forum  is the community website for the book How To Cheat in Photoshop, by Steve Caplin. It's a friendly and welcoming place to ask any Photoshop-related questions, to show off your work, and to hone your Photoshop skills by taking part in the weekly Friday Challenge . You don't need to own the book in order to use the Forum!

Adobe - it's hard to believe you don't have Photoshop if you've made it this far into the website, but this is the place to go to read about the latest version of the world's favorite image editing program.

Adobe Press are the publishers of 3D Photoshop , as well as a great many other relevant books about Photoshop and other Adobe products.