I've been working on a super-comprehensive list of issues that tie into Infinite Crisis, going way way back with backstory and precedent for a lot of what happened. For example, Eclipso has a long history of possessing very powerful individuals, including the Spectre at least once. Rann and Thanagar have come to blows before. Batman's efforts at keeping tabs on heroes have backfired before, most recently and notably in the Tower of Babel JLA storyline. The forces of magic have been tainted in a universe-threatening way before. And the Secret Six are hardly new to the DCU.
There's about 300 issues for basic backstory and precedent, maybe 200 issues occurring in what has been called the Prelude, the period between Graduation Day and Countdown Special. Then there's another 150 or so that either officially tied into Countdown to IC, or should have. And then there's a little less than a hundred issues taking place within the brief timeline of IC itself. After that is 52, which is of course incomplete right now, and the OYL story arcs. I also included a section that I termed "Ripples of Infinite Crisis," which includes the reboot of LoSH, which was a direct result of events that tied into IC, the 1,001 Years Later arc of LoSH, and WildStorm's Captain Atom Armageddon, which is not only a result of a Superman-Batman arc critical to IC, but has a profound impact on Captain Atom's behavior post-IC. It's a lot of comic books to read, but I'm a perfectionist/completist, and it provides the most well-rounded, accurate picture of the events and characters integral to Infinite Crisis, as well as really good background and understanding of why those events occurred, and why the characters behaved the way that they did.