sparkfun.com is a good start . There are kits, schematics, etc. available. The easiest way to find these is do an internet search. As a matter of fact, entering "how can i build a simple usb avr programmer" into Google yields more than 81,000 hits. And the best part is that you can do this on your own and you don't even have to wait for someone to reply. Instant gratification.
Depending on the programmer and this applies to PICs too, you'll either need a hard to source and solder without a proper PCB layout FT232(R) USB to serial adapter or a preprogrammed AVR or PIC designed specifically for the task.
Most homemade programmers use the printer port or serial port.