Surely a Trilogy is only a True trilogy when there is one story arc or major connection which joins the 3 movies together (which isnt just the central character?)
For Example the Indy films (and i Love the Indy movies, sans Crystal skull)are all seperate, stand alone stories... that was the intention when they were made, in the vain of older matinee adventure movies. The only connecting factor is the character.
Much the same as the Potc movies are not ALL part of the same story arc. The first 3 possibly are (at a stretch) but with the fourth the only connection was Jack Sparrow (and the franchise did not start out as "TheJack Sparrow Story")
The Dark Knight Trilogy works because it is the continuation of a bigger story arc.
Starwars.... is a tricky one. Im older and therefore count the original Trilogy as the greatest and the prequel trilogy seperatley... but i guess.. it is ALL one big story and so.. ..i dont know... I guess the prequels are anakins story and the original Lukes so there are 2 different trilogies there.
The Matrix... just got too messy for me.
Toy story is right up there (im assume everyone classes it as the ANdy Trilogy
Back to the Future, hmmmmm first two 10/10... the third... erm... not 10/10
I cant wait for a Dark Knight Marathon at home, with My buddies and Beers (Will send the wife out shopping for that one) I think that is when i will truely know where this story fits in my collection.