All under the sun ( :-)

With a wide variety of products, it might be confusing for a beginner.
So the first place to orient with the product line would be this document.
This document has some big tables, where in which you can see, what is what!
www.atmel.com/dyn/resources/prod_documents/doc4064.pdf
Maybe this will also help
http://www.ineltek.com/de/files/AVR_Product_Line_Reference_-_Dec08_-_Customer.pdf

Some info:

STK525 - A USB development board, with AT90USB128 micro controller on it.
We can program based on USB, RS232, Joystick, 4LEDs, Temperature, Microphone, DataFlashMemory(for USB Mass storage demo), Potentiomenter.
Might require STK-500, to use all the programmable ports of the MCU!

STK500 - This development board ships with a AT90S8515-8PC micro controller it.
But it provides slots into which we can place compatible MCUs of various sizes.
I can see that it provides 8 LEDs & 8 Switches.
10 I/O ports for parallel mode programming.
Can provide power supply to STK525, if it is placed over STK500.


AT90USBKey - Self contained stuff, Kind of a stripped down merge between STK525 & STK500