SparkFun's minimal design approach to Arduino. This is a 5V Arduino running the 16MHz bootloader (select 'Arduino Duemilanove w/ 328' within the Arduino software).
You need to wedge an Arduino into a really tiny spot? Simple - just use a SMD '328 IC. Oh... you want a reset, and voltage regulator too? Why didn't you say so!
Arduino Nano is a surface mount breadboard embedded version with integrated USB. You want a breadboard-friendly Arduino? This is it!