This is a counterrespone to this thread, which vouches for Dumbledore being alive..
http://forums.d2jsp.org/index.php?showtopic=6287614&f=266&st=75But I think Dumbledore is dead, and it WAS snape that killed him.
They agreed on this, and Snape didn't really want to do this, because Snape is a good guy!
Why:
Snape and Dumbledore obviously have been planning something, and Snape didn't want to do this.
Dumbledore trusted Snape with his life. When Voldemort (Tom Riddle) asked for the DADA job, he rejected him

Dumbledore is a good judge of character!
JK has stated that Dumbledore IS definetly dead. JK also said that in book 6, someone close to Harry would DIE.. Who else than dumbledore died??
Snape have had several chances to kill Dumbledore.. Why would he do this in front of other death eaters? To prove something perhaps?
Snape didn't want to perform the AV curse on him, when killing Dumbledore, and Dumbledore pledged for him to do it:
Quote
somebody else had spoken Snape's name, quite softly. "Severus..." The sound frightened Harry beyond anything he had experienced all evening. For the first time, Dumbledore was pleading. Snape said nothing, but walked forward and pushed Malfoy roughly out of the way. ... Snape gazed for a moment at Dumbledore, and there was revulsion and hatred etched in the harsh lines of his face. "Severus... Please..."
The hatred and revulsion Snape felt, was not for Dumbledore, but for Snape actually having to perform this. He hated himself for it.
Dumbledore is a pruod wizard who would on no account fear death.

Why would he beg? He would never beg Snape to spare his life (maybe beg him not to turn over to the other side), but more likely he would beg Snape to kill him. He knows how hard this is for Snape, but he begs Snape to kill him according to their plans
Snape killing dumbledore is part of a great plan that Dumbledore has made, and we will find out all about this in the seventh book.
Snape is good, and we haven't seen the last of Dumbledore.. But he is definitely dead, because JK has said this!