I recently watched a lot of DBZ movies thanks in part to Nicktoons airing them in between seasons of Kai, it was educational to say the least, as I had seen many of them before but long enough ago that my memory was rusty, and I never bothered trying to put them into continuity with the rest of DBZ until now, and was a bit shocked by the obvious plot-holes and continuity errors.
The un-disputed three that fit:
Bardock: Father of Goku: This one takes place prior to Dragon Ball, can't call it out on continuity errors because it is the beginning of the continuity
The History of Trunks: Serves as a prequel to the Android Saga, it takes place in an alternate reality, one that sets the tone for the android/cell sagas, so it fits.
Cooler's Revenge: The only thing that could be called a continuity error in this is Cooler thinks Goku killed Frieza and King Cold, I'd just cough this up to him being unaware of a time-travelling super-saiyan who actually killed them in Trunks and be done with it, and count this among the ones that fit.
Absolutely dont fit in continuity:
Super Android 13: Let's see how many errors I can pull off the top of my head:
1: This places itself after 17 and 18 were activated, yet Goku is not suffering from the viral heart dissease, which he showed symptoms of during his fight with 19, and was not free of until Cell became a major threat, he is also unaware Gero is dead, odd. So this can not take place prior to the Android saga. since Vegeta is an SSJ and Krillin is not surprised by that, Trunks is around, Goku is not sick, Gero is dead, Gohan is not an SSJ, this one is well... Somewhere around the two minutes before they were aware of Cell? Bad continuity error writers.
A slightly worse offender was Broly The Legendary Super Saiyan, not so much at a glance, but this one would have to take place during the 10 days leading up to the Cell Games given that Goku, Vegeta, Trunks, AND Gohan were all SSJ in this, and since Goku was dead after the Cell saga, I imagine this was written without that end in mind. So for this to work, during the 10 days everyone was busting their asses to train to fight Cell, they just decided to leave Earth and go on an adventure in space. And considering how closely DBZ followed that training, I doubt it.
Anyways just venting my thoughts, feel free to comment, expand, tell me I am wrong, whatever!
Edit: another minor nitpick was with Broly 2nd coming, when Goten recognized the spirit of his father Goku by his voice, there was only one time this movie could have occurred and that was during the time prior to the World Martial Arts tournament where Goten first met his father... Though guess you could just consider that a child knowing the love of a parent regardless of ever actually having met them.