General

Nanohub Nanotechnology

Society Of Robots Basic Robotics

Let's Make Robots

MathCS.org Robotics

Youtube/nptelhrd [v] Engineering

eFluids Fluid Mechanics

Gizmology Various notes on mechanical systems & projects

iCrank Various mechanical engineering design resources

Curious inventor Various guides on designing & metal working

Machinery's handbook[b] Must have for every engineer

Military machines Various manuals from the military (most likely US) on how to use, operate, etc. most weapons/systems/vehicles. Even has other educational material issued by the military here

Dr. James Calvert History & some Tutorials on Mechanical, Civil & Electrical

Bolts Big chart on all the different types of bolts & their uses

Engineering student Various resources for mechanical engineering students

Equipment List of equipment & processes & how to use them/how they work

Robot Books best way to learn to make robots, tons of books on how to design for beginners, etc. fucking five star post man if you want to learn robotics

The Scientist & Engineer's Guide to Digital Signal Processing

General F.E. Exam Prep Look for "Download FE exam specifications (PDF)"

M A T T E R Material science engineering and some physics

Electronics

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Lessons In Electric Circuits A free series of textbooks

U.S Navy Electricity & Electronics Training Series (NEETS) Contains 24 modules, each covering a specific topic in the field of electricity and electronics. 

Curious Inventor Guides This page contains lots of good guides for some skills like soldering and random ones like how the PS2 controller communicates.

Circuit Simulator Applet A neat Java applet that simulates multiple types of circuits and is customizable

Basic Electronic Tutorials Very informative tutorials on digital + analog electronics

Logicly A logic circuit simulator. It seems to require "PAYMENT" for full software. The trial/demo is pretty good by itself though

Technical Library Excellent website of more advanced projects.

Introduction to Digital Filters with Audio Applications- Julius O. Smith III Emphasis on audio and music applications, although the material on the subject of digital filters itself is not specific to audio or music.

Engineering video lectures (playlists)

Intro to Chem-E  (Stanford)

Electricity & Magnetism  (MIT)

Organic Chemistry  (Yale)

Thermodynamics & Kinetics (MIT)

Mech-E: Heat & Mass Transfer (Indian university)

Civil - Fluid Mechanics (Indian university)

Solid State Chem  (MIT)

Chem-E: Process Dynamics & Controls  (University of Michigan)

Materials Science (Indian university)

Introduction to Robotics (Stanford)

Core Sciences and Engineering (NPTEL) "Technical lectures from all seven Indian Institutes of Technology and Indian Institute of Science, Bangalore."

Tools / Reference / Exercises

engineeringtoolbox.com Engineering Reference/Tools

nrich.maths.org/stemnrich Engineering Challenge Problems

grantkot.com/MPM/Liquid.html Fluid Simulator

Engineering calculators various calculators dealing with problems in fluid dynamics, materials, design, etc.