I recently needed to encode a 32-bit value into something easy for QA folks to remember and report. I opted for 3 words out of an 11-bit (2048 entry) dictionary of commonly used words.
How to build the dictionary? Well, in order to determine the most commonly used English words, I downloaded a bunch of free texts from Project Gutenberg, and did some simple filtering - nothing less than 5 letters, no duplication of singular + plural, etc...
A valuable lesson that I learned during this process is that when your corpus includes older english texts, you should always give your final list a visual once-over and apply some judicious manual filtering. I'm looking at you, "The Adventures of Tom Sawyer". (And, to a lesser extent, Moby Dick).