How to: Testing for malfunctioning parts

Hey

I want to get a HOW TO going, with the help of our experienced and knowledgable members, about what the DIY can do to test for parts that should be replaced. Obviously, we'll have to keep it simple and just discuss mechanical parts. I'll send a message to the admins, and hopefully they'll make this thread a sticky.

So if you know a thing or two about cars, then please share the knowledge and try to keep the following in mind:
1. Symptoms you may experience while driving
2. State the part you're testing and its location
3. What you should do to test it
4. How does it differ from a functioning part

Just a small list to get things started:
1. tie rods
2. ball joints
3. pulleys
4. bearings
5. breaks (rotors, pads, calipers)
6. belts
Anything else is welcome, and I'm sure everyone would appreciate something like this.

Thanks for your time.