I had a brilliant developer work for me, and he wrote applications that have formed the new basis for what I do and will shape the future of the industry.
But what most people remember him for was a lookup in a shared spreadsheet that would pop up an email that was pre-addressed and pre-headed to highlight an issue, saving 300 people about 2 minutes of search 20+ times a day. He wrote it in about 20 minutes because he was annoyed at looking emails up manually.