Is dumbledore dead ?

Yes and No,

We will start with an excerpt,
DD's statement in Chamber of Secrets

-> ......“you will find that I will only truly have left this school when none here are loyal to me. You will also find that help will always be given at Hogwarts to those who ask for it.”......

What I deduce from the above statement is, DumbleDore is dead(or not dead) a part of his Soul (may be in the form of Horcrux) still remains at Hogwarts and wants to help who ever needs it.

Few qstns come up,
what about the unbreakable vow snape has made ?
Exhaustive analysis can be found at www.dumbledoreisnotdead.com