The Duinostamp is a convenient breakout board allowing you to easily embed an Arduino compatible environment into your project. The same size as a 34-pin 0.600" DIP, it's easy to incorporate into bread-boards, perf-board, or PCBs. It contains all the components and connections you need, without including costly and large extras.
This is a full kit including all the required components including a pre-programmed ATmega328.
See the project's webpage for more information.
For communication, you may want to try the USB-TTL w/ reset kit.