I present the Doctor Who crossover series by Phantazm. The characters are actually in-character, which is a good sign. Vader is honestly Vader-y, the Klingons are definitely Klingon, and the Doctor is actually acting like himself.

1. Is There A Doctor In The Quadrant? - Dr. Who/ Star Wars
http://www.fanfiction.net/s/4163934/1/IsThereaDoctorintheQuadrant

2. To Boldly WHAT! - Dr. Who/ Star Trek: TNG
http://www.fanfiction.net/s/4289930/1/ToBoldlyWHAT

3. Three Million Years For This! - Dr. Who/ Red Dwarf
http://www.fanfiction.net/s/4342232/1/ThreeMillionYearsforThis

WARNING: I am currently unsure as to my ability to seperate mediocrefic from goodfic, so don't get your hopes up too much.