As much as I like Matt Smith, David Tennant is the reason that I started watching Doctor Who. I still miss him and constantly go back and rewatch his episodes (yay for Netflix InstantWatch!) Here's a video of David's last day on the set of Doctor Who.
Here's a fun video that the cast and crew of Doctor Who made for David Tennant's wrap party.
Here's a picture of David from the very first episode of Doctor Who that I watched, "Doomsday."