Quite some time ago I designed a quick and dirty prototyping board based on the AVR ATMega16 microcontrollers. I find it useful enough so I decided to share the design here.
It is a fairly simple design with a couple of buttons, two LEDs and a RS232 level converter for interfacing with a computer. Additionally all the IO ports are available via headers and there is a jumper for selecting between 5 and 3.3 volt operation.
The design was created with the free tools provided by ExpressPCB
For programming the board I can recommend PonyProg, it is free and supports a wide range of programmable devices. The AVR ISP parallel port interface described on the ponyprog pages can be used to program the prototype board. It does however require a simple adapter cable as the pinout of the ISP connector on my board is slightly different.
Additional development tools such as debuggers, compilers etc. can be found on the AVRFreaks website. I used primarily WinAVR for my software development.
There is a bug in the PCB layout somewhere around D2 and D3. I don't remember what was wrong exactly but I have scraped and modified a few traces there so do double check it.