I would like to point out that the Council of Tent was the first time the Catholic Church put it's official stamp on the entire canon of the Bible, not just the deuterocanon. It might seem odd to us that it would take 1500+ for anyone to say what was or was not officially in the Bible, but up to this point, there was no serious question as to what belonged in the Bible and what did not among Western Christians until the generally accepted books of the Bible were questioned, rejected, and so on. Once this started, someone decided "hey, we gotta set some things in stone here before anyone else gets trigger happy." This at least prevented people from doing things like removing Revelations and the Epistle of James as Luther wanted to do originally.
I would also like to provide the definition of an indulgence since few people get it right, even today's average poorly informed yet self proclaimed Catholics:
An indulgence is something which does not forgive sins. It does not get anyone out of hell. When people would confess their sins, they would be given a penance, something to do to make amends. They were already forgiven by God, but amends still had to be made to the community (the Church, fellow Christians). Society was much more harsh and rigourous in the Middle Ages, so common penances would be to fast for a year, to wear the clothes of a beggar for a few years, to stand outside of the church before services so that you could show your guilt and humility as an example to others, and so on. These penances took a very long time and the danger of death in those days was rampant. You could catch the plague, and boom, dead. So, the idea of indulgences came about. What these did was remit the temporal punishment due for sin, ie, they shortened the time of penance. So, if my penance was to sit on the church steps with a sign that read "I stole from my neighbor" for a year, the indulegence might cut that down to a months time or do away with it altogether.
With the belief in purgatory, what an indulgence is believed to do is cut down the amount of purgation needed for one's soul in purgatory. Indulgences do not forgive sins, and they are useless to anyone in hell for people in hell have already rejected God's graces in life and have been judged accordingly. Idulgences may not be bought or sold, they are only merited from a sincere desire to amend one's life, to confess one's sins with a contrite heart, to do one's penance with humility and piety, and to worship Christ in the manner fitting to him.
Now, in the time of Luther, there were many individual priests and bishops, and probably the pope of that time, who had their eye on earthly things and not heavenly things. They took advantage of the sinful nature of man and man's desire to see heaven, and decieved the average joe by claimig that sins could be forgiven by pay, and that a way to heaven could be bought. This was wrong. It should not have happened, but it did happen, and Luther was justified in his digust for these abuses. Learned Catholics tend to have a high respect for Luther on this point. I just wanted to clear that up because a think a lot of people do not understand what an Indulgence is according to the real Catholic definition.