TITLE: Most understandable notes on Jacquet-Langlands?
QUESTION [13 upvotes]: I am particularly interested in the comparison of the trace formula part of Jacquet-Langlands. But I found the original text hard to read.

REPLY [6 votes]: I think that you may like the notes by Ioan Badulescu: see 
http://www-math.univ-poitiers.fr/~badulesc/pub/JLtata1.pdf
They are a 20 pages modern essentially complete exposition of the proof of Jacquet-Langlands not only for $Gl_2$ but for higher higher rank linear groups and their inner form as well.