One of the more annoying things about crystal-controlled micro-controllers is that the crystal circuitry employs something known as load capacitors. (Not true for circuits built with a ceramic resonator as the resonator has manufactured capacitance within the unit.) With the Arduino barebone circuits, two small load capacitors of values from 12pF to 22pF are usually specified and the value is based upon the specific crystal manufacturing process. Specific values are therefore in the manufacturer's datasheet.

Adafruit has a rather nice write-up on the subject if you require more information. 

http://blog.adafruit.com/2012/01/24/choosing-the-right-crystal-and-caps-for-your-design/

If I could just throw away everything except the crystal, then by barebones Arduino has a  total of just 2 purchased parts: uC and crystal.

Are the load caps not required? Yes, but we can actually make 'em right into the project with a little hacking. Remember, electronics and physics are eternally linked. The process to build a small capacitor is not unlike what was done back in 1745 when the Leyden Jar was created. Except in our case, our little capacitor (we will need 2 identical ones) will be just 7.10 mm wide and between 10.0 and 13.0 mm long. Instead of glass, we are going to use a marvelous tape known as Kapton selected for the high temperature thermal stability of the product.

Gallery pictures complete the project documentation.