Data from Star Trek. One might question whether this was really a death seeing that he was a machine, but on the other hand his being a machine added to his death being so unnecessary. Being not dependent on breathable air he could have very simply escaped the situation in which he died / was destroyed.
Technically Data didn't die. While his original body was destroyed, he transferred all his memories and thoughts into another android earlier in the movie and at the end of the movie the android was starting to emulate Data's behavior.
Want to talk about a totally pointless Star Trek death? How about the death of Spock in Star Trek 2? Yeah, it was sad and shocking, but they brought him back in the very next movie.
Also, the death of Kirk in Star Trek generations. He was later resurrected somehow in one of the books. (William Shatner wrote the book, by the way.)
