Is there a way to make wiring a bare microprocessor to a shield easier? I currently do most of my AVR work on breadboards, but the large variety of Arduino shields and code out there makes me wonder if I'm not beating my head against the wall sometimes, and looking up port to pin mappings both wastes time and slows me down. Is there any convenient way to adapt AVRs (other than those pin-compatible with current Arduinos) to Arduino shields?
You can make adapter boards (one for each mcu model).

The bottom side (male headers) would plug to the breadboard and the upper side would have female headers with the same pinout as an Arduino board (female hearers placed in the appropriate positions to match Arduino shields).

Such a board shouldn't be difficult to design.

Here is an image that resembles what I describe



It would adapt the pinout of a bare AVR to the pinout of a typical Arduino so that shields can by directly plugged on top of it.



Also a pinout diagram may come handy to speedup things when you use a bare chip with Arduino code.
(image source)


Another similar solution is a small printed sticker placed on top of the AVR
(image source)