Here are a few more links and ideas:
If you put both ATmega8 and 168 in the sockets there is an upgrade path there: if users get ATmega328 it takes place of the main Arduino processor and ATmega168 gets bumped into co-processor place. This adds value to your kit.
SparkFun released a new ATtiny2313 based ISP programmer http://www.sparkfun.com/commerce/product_info.php?products_id=9231
. No zenner diodes there only three resistors to interface USB.
Also, found today AVGA project at http://avga.prometheus4.com/index.php
. It is VGA/PAL/NTSC graphics output library for a 20MHz AVR Mega MCU. It runs on ATmega168, and may have limited capabilities on ATmega8. The DAC is implemented via 12 resistors and no diodes.
As a kit provider you don't have to implement any of this. But you can make prototyping area, enough for any of the cool projects, throw in all necessary resistors, caps and diodes, and provide URLs, schematics, and source code for all those projects.
I bet you are doing it already, but if not you definitely should make some sort of tutorial on how to use your kit and a step-by-step guide how to make various cool projects with available parts. At a very small cost this adds tremendous value to the kit.
Good luck Vikas, and keep us posted about your progress!