I decided to make an article about the Sack of Rome (1527) and earlier phases of the Italian Wars, but I lack primary sources and I don't have many good quality secondary ones. I would like to ask for sources for those events, specially for the Sack of Rome. Most of information you find about it resides in Wikipedia and some biased texts from religious apologetics (for example, comparing it with the Sack of Constantinople in 1204).

You can share internet links or texts you have in high esteem even if you doesn't regard them as a "secondary source". I also have some previous conclusions about these events:

I) Landsknecht brutality and behavior is often over rated to other fellow soldiery. When I read an Osprey's book about the Siege of Tunis (1525), the primary source quoted stated that Emperor Charles and the officers didn't trust in the spaniard and italian element of their army. And, unlike the latter, the landsknecht obeyed Charles' appeals to not pillage or destroy the city (at least they were the latest to starting pillaging after everyone did it). I believe the same logic could be applied for these campaign in Italy as well.

II) The devastion of the Sack is also over rated (for example compared to Constantinople), since the Papal States weren't exactly on their heels, and some years latter the Pope could AGAIN start trouble against the emperor. Only when the Duke of Alba put an army to march to Rome again he declined his military aspirations.

III) Spanish military behavior towards civilians and local cities might not have been that different than those of the french, but I don't have much to support that.

The artist Benvenuto Cellini served with the Papal forces during the siege. His autobiography is ... entertaining.. to say the least.

His experiences at the siege start at Chapter XXXIV:

http://www.gutenberg.org/cache/epub/4028/pg4028-images.html

Try Christine Shaw and Michael Mallett's Italian Wars 1494-1559: War, State, and Society in Early Modern Europe.