This project shows how to build a STK500 AVR ISP programmer with USB support. It uses FT232BL chip to implement USB to serial converter and ATmega8 in DIP package. This programmer is a clone of original AVR STK500 programmer, it works with AVRStudio and AVRDude and all main platforms including Windows, Linux, BSD and MacOS X. Check schematics and PCB on the link below.
STK500 compatible AVRUSB programmer - [Link]