While other DBZ movies just used whatever opening went with the show at the time the movie was release, Tree of Might features a specially-made opening, featuring the Z-Fighters gathering the Dragon Balls to restore the destroyed forest.
When Dragon Ball Z was first dubbed, the opening credits used a mix of footage from the series, from the first three movies, and the Japanese intro sequences. It was accompanied by an American-only theme song called Rock the Dragon. This intro was unusual in that it had footage from movies that never aired on TV at the time, and in that it showed many things that would not happen until much later in the series, and not as a part of this dubbed version (Future Trunks, short-haired Yamcha, Super Saiyan transformations, etc.)
The show has three openings. The first opening (Saiyan and Frieza Saga) is a montage of the characters and battles, and it features a scene of Nappa and Vegeta walking through fire, and ends with the Z-Fighters assembled, joined by Goku who falls from above wielding his Power Pole (unusual considering he never uses it in Z.) The second intro (Cell Saga) is basically the same, however it eliminates the "Nappa and Vegeta in fire" sequence, and shows a more modern group shot of the Z-Fighters at the end, including Goku becoming a Super Saiyan. The third intro (Buu Saga) is completely different and features a new opening song, with footage of the Z-Fighters as they appear later in the series. The first two intros are accompanied by an end credits scene of Gohan running on a globe, intercut with other footage of Z-Fighters and allies. The third intro has an end credits scene featuring Gohan walking down a sidewalk, looking up to see Goku with angel wings, who drops a feather from them.
When FUNimation aired the Buu Saga, their end-credits sequence used footage from the Japanese Buu Saga end credits. Strangely, they show the feather dropping from the sky, but they DO NOT show the Goku with angel wings who dropped it!