5. When the surviving members of the Woodbury army express a desire to return to Woodbury and leave the prison group alone, the Governor, while Martinez and Shumpert watch in horror, guns them down and executes them all except for Karen who pretends to be dead but survives. ("Welcome to the Tombs")
4. Upon learning of Andrea's departure, The Governor tracks her down and hunts for her in an abandoned warehouse. ("Prey")
3. Merle drinks whiskey and blasts Motörhead's Fast And Loose while leading a parade of walkers to the Governor's meeting place. ("This Sorrowful Life")
2. Morgan explains that his son, Duane, was bitten and infected by his turned wife, whom he had been reluctant to put down. Morgan explains that whenever he turned on his own walkie-talkie every day at dawn, Rick never had his on. Rick invites Morgan to return to the prison with the group, but Morgan refuses, not wanting to witness any more death. Morgan's mission, he believes, is to "clear" the world of walkers. ("Clear")
1. Rick learns of Lori's death and collapses in mourning. ("Killer Within") - Probably the best moment of the entire series to me; completely gut-wrenching
Honorable Mentions:
Rick breaks down to Lori over the phone, accepting her death and rejoining the group. ("Hounded")
After Tomas sets Rick up to die in the laundry room fight with walkers, Rick immediately kills Tomas. Andrew attempts to retaliate but finds himself outnumbered and flees into a walker-infested prison yard, where Rick leaves him to his fate. ("Sick")
Rick takes T-Dog, Daryl, Glenn, Maggie, and Hershel get separated inside the prison tombs. While searching for Glenn and Maggie, Hershel gets bitten on the lower leg by a walker. ("Seed")
Rick, Daryl, T-Dog, Glenn and Maggie fight off walkers outside the prison. ("Seed")
Rick is cornered by the incoming walkers with his back pressed against the outside prison fence but is saved by Daryl and Merle. ("Home")