This schematic shows the Atmel ATmega8 circuit as it was built on its test board. The ATmega8 is using an external crystal at 16 MHz. There is also an ExpressPCB design file for a full 28-pin AVR development board that supports the ATmega8, and other ATmega microcontrollers. Please note that the ATmega8 is not functionally or software compatible with the x8 family, but it is pin compatible. For instance (from the ATmega8 datasheet):
The ATmega8 is an old part, and there are "upgraded" versions in the ATmega88, ATmega168 and ATmega328 MCUs. I used the ATmega8 in the serial terminal because it is still the most popular ATmega microcontroller. See a comparison between the ATmega8 and the ATmega88 for some specific differences between them.
Here you can find the current ATmega8 datasheet
This is an ATmega8 circuit with a crystal added. The actual test circuit for the ATmega8 was a serial terminal project using the ATmega8 to read and decode a PS/2 style keyboard and update a 2 x 16 LCD display. Here is some ATmega8 PS/2 keyboard code. There is also a PS/2 keyboard tutorial using an ATtiny4313.