I got into the Doctor Who game late, so this may be old news to all of you, but I stumbled onto some fantastic Ten/Donna fic which I've never before seen on any rec list, so I figure it's worth spreading the news.
It's an alternate season 5, Ten/Donna fixit adventure, 4 complete stories and one ongoing. It's written as friendship but veers towards shipping, really. I am usually not an adventure-type fan, so when I find one that really gets me, I'm very impressed. Note: the originals were written in Polish, so this is not the author's first language -- the first story in the series shows this a little bit, but as you read on the translation improves drastically and, really, the stories are so good that all is forgiven:http://www.fanfiction.net/u/1845671/HermitsUnited
The first story in the series is "Past Future Continuous."
P.S. the author also has a great ongoing Supernatural/Who crossover.
And, probably better known but I'm throwing in in here anyway in case you haven't read it, Alcibie at http://www.fanfiction.net/u/824120/Alcibie
has a Ten/Donna adventure/fixit series that I re-read constantly.
If you've missed these two authors before, you're in for a treat and a long night of reading! If you already know about them...well why didn't you tell me earlier?! :P