Easy way to keep track of your little one's vocabulary development

This is a bit random, but a question from a friend today about baby's first words reminded me of this and I wanted to share the idea in case anyone else finds it handy.

As my boys started learning how to talk, we would jot down their new words on a dry erase board on their door, and then I took a picture of it every so often to document. It was an easy way to keep track of their vocabulary development, both for sentimental value and to make it easier to answer those milestone "How many words does your child have?" questions at the 18m and 2 year visits. :) Here's a sample picture of the dry erase board taken when they were about 19 months: