Processors

http://en.wikipedia.org/wiki/ARM_architecture

Used in majority of smartphones.

http://en.wikipedia.org/wiki/X86

Electronics

http://en.wikipedia.org/wiki/Bug_Labs

Udoo: http://www.kickstarter.com/projects/435742530/udoo-android-linux-arduino-in-a-tiny-single-board

http://www.pcduino.com/

http://blog.makezine.com/2013/04/15/arduino-uno-vs-beaglebone-vs-raspberry-pi/

Arduino

Single-board microcontroller based on Atmel's ATMEGA8 and ATMEGA168 AVR microcontrollers. Arduino is a fork from the Wiring development platform.

http://en.wikipedia.org/wiki/Arduino

Official resources:

http://arduino.cc/

Introduction: http://www.arduino.cc/en/Guide/Introduction

FAQ: http://arduino.cc/en/Main/FAQ

Foundations: http://arduino.cc/en/Tutorial/Foundations

Language reference: http://arduino.cc/en/Reference/HomePage

Arduino products: http://arduino.cc/en/Main/Products

Distributors: http://arduino.cc/en/Main/Products

Tutorials: http://arduino.cc/en/Tutorial/HomePage

Getting started: http://arduino.cc/en/Guide/HomePage

Software: http://arduino.cc/en/main/software

Runs on Windows, Macintosh OSX, and Linux operating systems.

http://arduino.cc/en/Reference/HomePage

Raspberry Pi

http://www.raspberrypi.org/

http://en.wikipedia.org/wiki/Raspberry_Pi

http://www.itavisen.no/nyheter/raspberry-pi-er-helt-fantastisk-4976

Official downloads: http://www.raspberrypi.org/downloads

Unofficial wiki: http://elinux.org/RPi_Hub

Quick start guide: http://www.raspberrypi.org/wp-content/uploads/2012/12/quick-start-guide-v1.1.pdf

Official forum - basic setup and usage: http://www.raspberrypi.org/phpBB3/viewforum.php?f=26

Buying guide: http://elinux.org/RPi_Buying_Guide

FAQ: http://www.raspberrypi.org/faqs

Introducing the raspberry pi - getting started: http://www.h2g2.com/approved_entry/A9143796

Introducing the raspberry pi - peripherals you'll need: http://www.h2g2.com/approved_entry/A13413584

Raspberry Pi Stack exchange: http://raspberrypi.stackexchange.com/

The Pi Hut - accessories: http://thepihut.com/

"The true cost of Raspberry Pi - essential accessories": http://www.penguintutor.com/blog/viewblog.php?blog=6354

https://www.modmypi.com/

Gotcha's and new users tips: http://www.keyboardmaven.com/2013/04/raspberry-pi-gotchas-and-newbiebuyer.html

Boots from SD card (Not included in price). Minimum size 2 GB. Minimum 4GB recommended. Pre-loaded SD cards can be bought. (for example: http://www.amazon.co.uk/For-Raspberry-preloaded-operating-partitioned/dp/B008IU78EK) If not, an SD card reader is needed to prepare the card. High-speed category 4 is recommended. See http://elinux.org/RPi_Easy_SD_Card_Setup and http://elinux.org/RPi_SD_cards
Programs must be compilable for ARMv6 architecture. (Windows/x86 not supported)
Video output through HDMI or Composite. No VGA.
Power through micro USB port. Standard phone charger with micro USB plug can be used (minimum 700mA at 5 volts).
No Real Time Clock (RTC) on board. Time is updated over internet after each boot.
Not all peripherals (keyboards, mice, etc.) may work (may draw too much power). See http://elinux.org/RPi_VerifiedPeripherals
Two models: A and B. B model draws 3.5 W, the A model 2 W.
B model specifications: 700 Mhz ARM1, 256 MB SDRAM

http://elinux.org/RPi_Hardware_Basic_Setup#Prepared_Operating_System_SD_Card

Applications:

http://www.digi.no/914772/denne-kontrolleres-med-rasperry-pi

http://www.theregister.co.uk/2013/03/14/feature_ten_raspberry_pi_projects/

Books:

Gray Girling: Rapsberry Pi Owners workshop manual: http://www.amazon.co.uk/Raspberry-Pi-Manual-practical-revolutionary/dp/0857332953

Mike McGrath: Raspberry Pi in easy steps: http://www.amazon.com/Raspberry-Easy-Steps-Mike-McGrath/dp/1840785810

Review of Raspberry pi books: http://www.theregister.co.uk/2013/04/18/feature_getting_into_the_raspberry_pi_books/

Richardson & Wallace. Getting Started with Raspberry Pi. Published December 2012: http://shop.oreilly.com/product/0636920023371.do

Upton & Halfacree: Raspberry Pi User Guide: http://www.amazon.com/Raspberry-User-Guide-Gareth-Halfacree /dp/111846446X Published September 2012. Somewhat dated already?