You could say I overthought this “minimal” ATmega328 µcontroller build: switchable USB/external power, reset button, optional D13 LED for your blink() needs, high efficiency LM2940 LDO voltage regulator …
In the age of cheap 32-bit microcontroller boards available for a couple of dollars, there’s absolutely no reason to build one of these semi-custom 8-bit Arduino clones. I did it because I had all (well, nearly all —the 0.33µF tantalum cap needed on the output side of the the regulator I bought in) the bits in the house, and I wanted to see how few connections a modern microcontroller really needed. Once I’d seen just how few, I thought I’d make this thing easy to use … and got a bit carried away.
The EMSL breakout boards are really easy to work with, though they are thin and need care when soldered lead-free. The Minimalist Arduino (archive copy) is a good start, or you can work through the derived Instructable: Arduino from Evil Mad Scientist ATmegaxx8 Target Board.
I do kind of miss the diversity of form in the µc board market these days. Everything looks like an Arduino now. Tiny variants like the Solarbotics Ardweeny kept creative interest up. But with boards and chips so cheap these days, why bother?