Sure Electronics (China) sells a 12 MHz ATmega 16 board for about $26, shipping included (check for good prices on eBay). It has a 20x2 character LCD, 4 digit seven segment LED display, 4 LEDs, 2 switches, an LM75 temperature sensor, a piezo speaker, and a 512 byte external EEPROM. It uses USB for RS-232 virtual com port communications and power.
The board is programmed via a 10 pin ISP connector. A user manual with (out of date) schematics and some sample code are available from Sure.
This project includes a discussion of the board, and source code to support every one of the resources listed above. The most interesting part of the code is interrupt driven TWI support for the LM75 and EEPROM.