General

ITP Physical Computing tutorials
Several tutorials around Physical Computing

MAKE: How to make PCBs
Collection of resources and guides

Sparkfun Tutorials
Tutorials on electronics design including EAGLE and SMD soldering

OpenCircuits
Wiki for sharing open source electronics knowledge, schematics, board layouts, ports and parts libraries

MassMind
Wiki tech reference around learning to design and produce PCBs

Complete Beginners Guide to the Arduino
A lot of Arduino example projects explained in every detail

Physical Computing (Book)
An introduction to Physical Computing by Dan O'Sullivan, Tom Igoe

Making Things Talk (Book)
Practical Methods for Connecting Physical Objects
By Tom Igoe

Getting Started with Arduino (Book)
An introduction to the Arduino open-source electronics prototyping platform by Massimo Banzi

Fashioning Technology (Book)
A DIY Intro to Smart Crafting
By Syuzi Pakhchyan

Hands-On Introduction to Electrical Engineering Lab Skills
More in-depth electronics from MIT Open Course Ware

PCB Design

PCB Design Tutorial
A popular quick guide on learning how to design PCBs, by David L. Jones

Build Your Own Printed Circuit Board
Effective book that covers the full process from design to production, based on EAGLE, by Al Williams

PCB Manufacturing

Makezine: "PCB"
Lots of how-tos around manufacturing PCBs on your own

Instructables: "PCB"
Lots of how-tos around manufacturing PCBs on your own

Lady Ada: Etching In-House
Semi-professional etching tutorial

Wikibooks
German How-To "Platinen selber herstellen"

Glossaries

EDA terms
Terms used in Electronics Design Automation (which is essentially what Fritzing does) are explained at EDA Consortium, EETimes

PCB terms
Glossaries of terms used in designing and manufacturing Printed Circuit Boards can be found at Golden Gate Graphics, PCBpro, SunMan

Electronic symbols
Overviews of symbols for electronical parts used in schematic diagrams can be found at Electronics Club, Wikipedia (German)

Assembling & Soldering

Surface Mount Soldering Tutorial
A detailed how-to by Sparkfun

Soldering Basics
Short and with pictures

SMT Soldering
Another one, with good pointers to videos