Piconomic Design is a small firm which had created nice course for learning AVR 8 bit microcontrollers. They have prepared a development board which you can by for 44.99$ or you can build one for non commercial purposes, because they made PCB and other files available on their website(one successful board replication is here).
Board have most of all necessary features ar pins that allows to cover almost all Atmega128 functionality.
Also Piconomic Design have prepared wonderful set of tutorials and even code AVRLIB for fast application development. All programming is done by using OpenSource WinAVR tools. I think this is nice example how commercial product can be delivered to end user – you want to try, grab it for free. Liked it? then be honest to buy.