Yeas,Albus Dumbledore is alive
Check out this site please.
www.dumbledoreisnotdead.com
The one theory I liked was that the person who died was not DD.
This comes from the Pensieve.
When DD shows Harry how to use a Pensieve in the Goblet and the Order,he always removes his own memories from his temple.
Even Severus Snape does the same while teaching Occlumency.
Agreed that DD showed Harry memories of other ppl,but when he showed Harry his own memory,the one in which he refuses the job to Voldemort,he takes the memory from the bottle.,
So,who is this person ?
Aberforth ?