The ATtiny25, ATtiny45 and ATtiny85 (and ATtiny13a) are the smallest AVR chips and they are all pin compatible. It is an easy and inexpensive way to get started. I created a basic breakout board and some shields to demonstrate how to program these small, but powerful chips.
20 LEDs Charlieplexed. Needs a board and a bridge.
19 LEDs Charlieplexed. Needs a board and a bridge.
This simple shield turn the board into a full-fledged TV-B-Gone.