There were several series that directly led up to Infinite Crisis while others had a bearing on the series or some historical significance.

Countdown To Infinite Crisis

 Day Of Vengeance
Rann-Thanagar War

The OMAC Project
The Return Of Donna Troy

Villains United
Crisis Of Conscience

Crisis On Infinite Earths
Graduation Day

Identity Crisis
Infinite Crisis Secret Files & Origins

Planet Heist
Power Trip
Public Enemies


The Insiders

 The Kingdom