PIR - passive infra-red sensor.
LDR - control a blinking LED with a light dependent resistor (LDR).
HBridge - used to reverse the polarity of a motor.
Servo - control an RC (Radio Control) servo with a potentiometer.
Transistor - build a circuit that will protect your Arduino when using an inductive load.
Stepper - drive a stepper motor with an Adafruit Industries Motor Shield.
A stepper motor (or step motor) is a brushless, synchronous electric motor that can divide a full rotation into a large number of steps. The motor's position can be controlled precisely, without any feedback mechanism.
http://itp.nyu.edu/physcomp/Labs/Servo - Control a servomotor's position using the value returned from an analog sensor.
http://www.makingthings.com/documentation/how-to/stepper-motor - You want to connect a stepper motor to the Make Controller Kit with an Application Board.
http://www.imagesco.com/articles/picstepper/02.html - Stepper motors consist of a permanent magnet rotating shaft, called the rotor, and electromagnets on the stationary portion that surrounds the motor, called the stator.
http://www.doc.ic.ac.uk/~ih/doc/stepper/others/ - Other stepper motors.
http://www.cs.uiowa.edu/~jones/step/types.html - Stepping motors come in two varieties, permanent magnet and variable reluctance.
http://www.piclist.com/techref/io/stepper/wires.htm - Stepper motor wiring.
http://www.jasonbabcock.com/computing/breadboard/unipolar/index.html - use this method to work out stepper motor wiring.
Mechanisms are used to convert between one type of motion and another. Any machine can be looked on as a group of interconnected mechanisms which convert one type of motion to a variety of other motions.
http://flying-pig.co.uk/mechanisms/index.html - From paper mechanisms to animated characters.
http://www.brockeng.com/mechanism/index.htm - Virtual mechanisms animated by Java.http://sprocket.telab.artic.edu/ed/DisplayCase/index.html - Electronics and Kinetics Technical Resource.
http://kmoddl.library.cornell.edu/index.php - A collection of mechanical models and related resources for teaching the principles of kinematics--the geometry of pure motion.
http://www.sdp-si.com/D757/Libdownload.htm - Comprehensive data about the design and selection of mechanical drive components.
http://www.cs.cmu.edu/~rapidproto/mechanisms/tablecontents.html - Introduction to Mechanisms.
http://en.wikipedia.org/wiki/Category:Mechanisms - 53 pages of mechanical devices with two or more interconnected parts that perform useful functions.
http://www.tigoe.net/pcomp/machines.shtml - Lever, Pulley, Gear, and Cam.
http://www.tigoe.net/pcomp/machines2.shtml - Joints and Linkages.
http://www.societyofrobots.com/ - Not sure where to start? My first robot tutorial.
http://www.instructables.com/id/How_to_Make_an_Arduino_Controlled_Servo_Robot_SER/ - What better way to start experimenting with open source micro-controllers (Arduino) than by building your very own open source robot?
http://www.parallax.com/ - Parallax designs and manufactures microcontroller development tools and small single-board computers.
http://www.arrickrobotics.com/index.html - a small company based in Tyler, Texas where all products are designed and built.
http://letsmakerobots.com/start - How to make your first robot.
http://www.robotstore.com/ - Jameco robotics.
http://www.vexrobotics.com/ - The VEX Robotics Design System (SolidWorks files of components).
http://www.openservo.com/ - OpenServo is an open community-based project with the goal of creating a high quality digital servo for robotics.
http://www.trossenrobotics.com/ - Providing customers with a one stop robot shop and superior customer service since 2005.
http://societyofrobots.com/axon/ - With the Axon, you will no longer need to worry about not having enough I/O as it has 55+ for you to use - up to 16 ports for analog sensors, and up to 18 for interrupts.
http://www.pcbexpress.com/ - Quick-Turn Prototype Circuit Boards.
http://www.maxbotix.com/ - Ultrasonic rangefinders.
http://www.mpja.com/ - Electronic components and more.
http://www.mouser.com/ - Electronic components and more.
http://www.seetron.com/ - LCDs and VFDs.
http://www.acroname.com/ - Robotics components.
http://www.atmel.com/ - Microcontroller chips.
http://www.figarosensor.com/ - Gas sensor manufacturer.
http://www.interlinkelectronics.com/store/store/?action=dsp_store_category_display&categoryID=217 - Force sensing resistors.
http://www.maxim-ic.com/ - A worldwide leader in the design, development, and manufacture of analog, mixed-signal, high-frequency, and digital circuits.
http://www.phidgets.com/ - Phidgets are a set of "plug and play" building blocks for low cost USB sensing and control from your PC.
http://www.wiring.org.co/ - Wiring is an open source programming environment and electronics i/o board for exploring the electronic arts, tangible media, teaching and learning computer programming and prototyping with electronics.
http://www.basicmicro.com/ - USB Universal Development Board works with all BasicAtom and BasicAtom Pro modules.
http://www.allelectronics.com/ - Electronic components and more.
http://www.goldmine-elec.com/ - We specialize in purchasing inventory lots directly from manufacturers and companies that build electronic equipment.
http://www.robotmarketplace.com/ - Robotics components and platforms (excellent range of motors).
http://www.roboticsconnection.com/ - Programmable robot kits, components, and hardware.
http://www.superdroidrobots.com/ - A wide range of robot kits, packages, and parts.
http://www.cs.cmu.edu/~chuck/robotpg/robo_rsrc.html - Chuck Rosenberg's Carnegie Mellon robot parts page.
http://www.battlekits.com/robot_motors.htm - Our motors have been specifically designed and battle-hardened for use in the robot combat competitions.
http://www.robotpower.com/products/osmc_info.html - Open Source Motor Control (OSMC) Product Information.
http://www.techbotics.com/acatalog/robot-servos-motors.html - Robot, robot kit and robot parts retailer in the UK.
http://servocity.com/html/how_do_servos_work_.html - an overview of how servos operate and how to communicate with them.
http://www.cnczone.com/forums/showthread.php?t=76865.#3 - CNC basic primer.
http://www.kelinginc.net/ - High-Torque Stepper Motors, Drivers, Planetary Gear Stepper Motors, Special-Type Stepper Motors, such as IP65-Rated Stepper Motors, DC Servo Motors, Power Supply, Spindle, ATC Spindle and other Components.
http://www.firstcadlibrary.com/ - CAD library of robot components.
http://www.eleinmec.com/index.asp - Articles on motor control, components, and practical matters like soldering, along with full shopping lists for each circuit described.
http://www.cs.uiowa.edu/~jones/step/ - This tutorial covers the basic principles of stepping motors and stepping motor control systems, including both the physics of steppers, the electronics of the basic control systems, and software architectures appropriate for motor control.
http://roborobert.com/2008/03/arduinos-servos-batteries-oh-my.html - Control more than 2 servos with your Arduino.
http://www.contraptor.org/ - A DIY open source construction set for experimental personal fabrication, desktop manufacturing, prototyping and bootstrapping.