Vol. 1 – Justice League International

Justice League 1–4
Justice League Annual 1
Justice League 5–6
Justice League International 7–13
Suicide Squad 13
Justice League International 14
Justice League International Annual 2
Justice League International 15–24
(at this point, the Leauge splits into America and Europe branches; Volumes 2 & 3 run concurrently to each other)

Vol. 2 – Justice League America

Justice League International 25 (trust me, it goes here)
Justice League America 26–30
Justice League International Annual 3
Justice League America 33–42
Justice League America Annual 4
Justice League America 43–51

Vol. 3 – Justice League Europe

Justice League Europe 1–6
Justice League America 31
Justice League Europe 7
Justice League America 32
Justice League Europe 8–19
Justice League Europe Annual 1
Justice League Europe 20–28

Vol. 4 – Justice League: Breakdowns

Justice League America 52–53
Justice League Europe 29
Justice League America 54
Justice League Europe 30
Justice League America 55
Justice League America Annual 5
Justice League Europe Annual 2
Justice League Europe 31
Justice League America 56
Green Lantern 18
Justice League Europe 32
Justice League America 57
Justice League Europe 33
Justice League America 58
Justice League Europe 34
Justice League America 59
Justice League Europe 35
Justice League America 60
Justice League Europe 36
Secret Origins 33–35

Vol. 5 – Justice League: Loose Ends (or More Injustice)

Justice League Quarterly 1–4
JLA 80-Page Giant 1 (“Mousebusters”)
Formerly Known as the Justice League 1–6
JLA: Classified 4–9 (“I Can’t Believe It’s Not The Justice League”)
DC Retroactive: Justice League of America – The ’90s

(I only included the DeMatteis material from JLQ 4.)

To clarify why JLI 25 goes at the beginning of the JLA book, it really is a JLA issue in all but title graphic. It’s the beginning of the Blue Beetle arc that goes through the next few issues of JLA, and if you have the issue in hand, you’ll see that JLI 24 is the best ending point for Vol. 1.