This is a list of various project resources.
Dave Jones and Chris Gammell discuss electronics in an off-the-cuff format. Discussions range from hobbyist electronics to the state of the electronics industry.
SparkFun - Lots of cool boards and designs to choose from. Plus many of the parts they sell have EagleCAD libraries for download.
Printed Circuit Boards
EagleCAD - The EAGLE Layout Editor is an easy to use, yet powerful tool for designing printed circuit boards (PCBs). The name EAGLE is an acronym, which stands for Easily Applicable Graphical Layout Editor. The program consists of three main modules; a Layout Editor, Schematic Editor and Autorouter which are embedded in a single user interface. Therefore there is no need for converting netlists between schematics and layouts.
Eagle PCB Schematics Tutorial - For getting started with EagleCAD I think this one is one of the best tutorials to use. It is now hosted by SparkFun which is related to their off-shoot service BatchPCB. Once you have mastered that move onto another tutorial Better PCBs in Eagle which provides handy rules, DRC and CAM files for making your own PCBs using SparkFun internal guidelines. Their design guidelines only cover the basics but I have found that following them has gone a long way to making very good PCBs reliably.
ESawdust - To use Eagle, you'll need parts, lots of parts. I found this site to be particularly helpful in finding various parts (or at least similar ones I can modify). Definitely the first place you should check when you need parts in your schematic. Also don't forget about the plethora of libraries and user language programs (ULPs) or scripts available at CadSoft itself.
Eagle Library Design - At some point you'll need to create your own part libraries for Eagle. I found this link to be helpful when creating new library parts in EagleCad. In general the best process always starts with the most similar part you can find, then modify it to suit.
BatchPCB - I have used BatchPCB for years. The process is quite easy and has nicely evolved over the years. They are very easy to work with and the quality of the boards you get back is very good. I have never had a problem with anything I submitted to them (except for my own mistakes!). They do have an initial-cost to overcome, but their pricing model is simple; by the square inch. I highly recommend them.
Free DFM Checking - I always run my designs through this site to get at least another set of "eyes" to look at it. It has caught some problems before, usually a bit too aggressive as it often complains about silkscreen line thinkness problems which for me are not really problems, but it is a great way to catch any of those last minute "gotchas".
ViewMate by Pentalogic - A great free tool for viewing Gerbers. It does require registration but it's worth it. Aparently their site also offers free upload DFM checks, but I havn't tried it to know if it is any good. Might be another good design checking resource.
Groups and Organizations
A group which exists for the purpose of dissemination of knowledge of the theory and practice of all aspects of robotics, including mechanical and electrical engineering, computers, electronics, radio, allied branches of engineering or the related arts and sciences.
An organization of model railroaders, that advances the worldwide scale model railroading community through education and standards as well as advocacy and fellowship.