I may be the only person who didn't know about this, but I was sure such a list had to exist, and I have had no luck in the past web searching for it. Now I stumble across it while clicking through Atmel's website:
A Parametric (i.e. sortable by feature) List of all the 8-Bit AVR chips.
For example, I've been looking through data sheets trying to figure out which AVR has both SPI and UART hardware in the smallest chip footprint. Peripherals like this don't make it to the "Product Card" page, and I've found that some of the AVRFreaks device summaries are just plain wrong!
You can also download an Excel spreadsheet of the list. If you like, wait until you have the list sorted like you want it, then download the spreadsheet. It's either auto-generated to match the displayed table layout, or they have one lying around of every possible permutation. Either way, it makes my life easier!