I beat SparkFun! :)

SparkFun sells a small board that will adapt a 6 and 10 pin AVR ISP connector to a breadboard. I had been using a special cable that I made with a 14 pin DIP IDP plug on one end and the 10 pin 2x5 IDP socket on the other end. That works because the DIP plug can split the center channel of a breadboard. But I do think that SparkFun's answer is a touch cleaner. What bugged me was the prospect of a 95 cent order with, like, $2 in shipping. So I sat down with Eagle and at the end of the day I made a design that costs $2.80 for a batch of 3 (so 93.3¢ each and free shipping) from OSH Park! That works out nicely because it means that I can permanently breadboard an ATTiny85, an ATTiny84 and an ATMega328P all at the same time for prototyping and pick the appropriate one for the design I'm working on. Each can have the power supply (with bypass cap), an i2c bus connection to a display shield, and ISP all ready to go - sort of like a poor man's Arduino.

If you want a batch of them, they're here.