The Doctor From Gallifrey 

The Infinite Quest: Set around the same time as Series 3, this 45 minute animation sees the Doctor (David Tennant) and Martha (Freema Agyeman) follow clues across alien worlds to find the Infinite, a legendary lost spaceship. You can watch it here.

Dreamland: Set around the same time as The Specials. America, 1958. The Doctor (David Tenannt) becomes involved in an alien war being fought inside the US military base known as Dreamland. An army of aliens is hatching beneath the New Mexico desert. Watch it here

Both are well worth a watch if you've not seen them before and if you can't watch them on BBC iPlayer or do and like them, they are both available on DVD.