Update Nov. 14/12: I was asked where Wolverine and the X-Men #18 would fall and that's before Avengers vs. X-Men. Since it's a one-off issue focusing on Doop and seemingly takes place before the event, I would stick it right after issue eight of that series. A little confusing on Marvel's part, but, hey, no surprises there.
Update Aug. 17/13: In doing a read of the event, I changed the placement of tie-in issues previously situated between Avengers vs. X-Men #7 and 8. Some tie-ins were moved prior to issue 7 and some were moved after issue 8.