From the department of life’s little improvements Google adds a contact picker to Gmail. You could always auto-complete from the composition window, but this is definitely an elegant improvement particularly when choosing several people to email at once, or if you have a very large contact list.
Other Google products like Google Docs and Calendar have had this for a while, but it’s nice to see it in Gmail. I’m hoping this means they will be soon supporting external address books in the enterprise Google Apps. One of the few down sides to moving to Google Apps at Pepperdine is the loss of the Global Address List.