First, be sure that you are handling the second edition of Haag's book!
I can also suggest H.Araki's book Mathematical Theory of Quantum Fields which is a bit more mathematically detailed than Haag's book, but covers a smaller area.
The very recent Advances in Algebraic Quantum Field Theory including the contributions of many authors (including myself). Some chapters are quite introductory and could be of help for you.
As a general source, have a look at this page Local Quantum Physics Crossroads: Bibliography. It contains several books on the subject of local quantum theories, including AQFT.
See also this page of the AQFT group of Hamburg AQFTlecturenotes especially the last lecture notes by K.Fredenhagen. Klaus adopted those lecture notes in his courses before retiring.
