Who were the first members of the justice league of america?

The founding members if the JLA are Superman, Batman, Wonder Woman, the Flash, Aquaman, the GL, and Martian Manhunter.
Others like Green Arrow and Black Canary joined later on.
Remarkably, all of the founding members of the past remained the founding members in the New 52 (at least there's SOMETHING it didn't fu** up)

The original JLA consisted of 7 members - Superman, Batman, Flash, Green Lantern, Aquaman, Wonder Woman and Martian Manhunter. Honarary member Snapper Carr was also featured in many early issues.

The team added Green Arrow (issue 4), Atom (14) and Hawkman (31) - before losing Wonder Woman in issue 69 and then Martian Manhunter in issue 71. Metamorpho turned down the offer of JLA membership in issue 42.

Black Canary joined what became known as the satellite era League in issue 75 before Snapper Carr was tricked by the Joker into revealing where the JLA's secret HQ was in issue 77 - leading to Snapper's resignation.
Other heroes to join the team were;
Phantom Stranger # 103
Elongated Man # 105
Red Tornado # 106
Hawkgirl #135
Zatanna # 161
Black Lightning # 173
Firestorm # 179