I would get the Blue and Gold Mini series from last year.
Giffen and DeMatteis reunited to write the second Booster Gold series from #32 to #43. Beetle, Mr. Miracle, Barda, and Power Girl all appear in it, and it ties into Justice League: Generation Lost, which was coming out at the same time.
That entire Booster Gold series is good. Geoff Johns wrote the first twelve issues (#1-6, 0, 7-10, and 1,000,000), which are excellent. A major story arc involves Booster trying to save Beetle's life through time travel. Then Dan Jurgens wrote #11-31, then Giffen and DeMatteis took over, and Jurgens returned to write #44-47, where the book ended.
People have already mentioned some of these:
Formerly Known as the Justice League #1-6
JLA Classified #4-9 (I Can't Believe It's Not the Justice League)
DC Retroactive: The '90s: Justice League #1
JLA 80-Page Giant #1 (just a short story)
JLA: Incarnations #6 (JLI flashback written by John Ostrander)
Martian Manhunter #24 (JLI flashback written by John Ostrander)
Mister Miracle #1-28 (the second series from the early '90s, which ran concurrently to JLA and JLE; I especially recommend #7-8)
Justice League: Generation Lost #1-24 (by Judd Winick and various artists)
Blue and Gold #1-8 (by Jurgens and Ryan Sook)
Human Target #1-12 (by Tom King and Greg Smallwood; the JLI find themselves in the middle of a neo-noir murder mystery)
Justice League 3000 #12-15 (Giffen and DeMatteis wrote the whole series, but Beetle, Booster, Ice, and Fire show up in these issues, and in some of the Justice League 3001 issues that followed)
Author of the law review article "The Lawyer as Superhero: How Marvel Comics' Daredevil Depicts the American Court System and Legal Practice," Capital University Law Review, Vol. 47, No. 2 (2019).
Download it for free at https://papers.ssrn.com/sol3/papers....act_id=3389544
There was also The Weird #1-4, which came out during the first year of JLI, written by Jim Starlin.
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