I am proudly presenting my world smallest arduino !
This bard contain micronucleus bootloader and is compatible with Digispark IDE, You can replace bootloader to Trinket / Gemma.
On-board is RGB led for your first experiments and transistor for driving relay.
http://www.ebay.com/itm/321298227959?var=&ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649
If you prefer breadboard friendly design I working on most versatile board.
Programmable over USB / ISP / Arduino as ISP
http://www.ebay.com/itm/321304411339?var=&ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649
bonus: 20 led charlieplexing module
http://www.ebay.com/itm/221354814659?var=&ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649