Columbia + 5
5 years ago was the Columbia accident. Some scientists have always decried the cost of human spaceflight, so Columbia's last flight was a research mission. Because of different orbits, Columbia could not have docked with ISS. However, at the time Atlantis was being prepared for flight. If some safety protocols had been ignored, she could have been launched on a rescue mission. What an adventure that would have been, one spacecraft on a risky flight to rescue another while the whole world watched.
In its aftermath we have a new Vision for the Moon, Mars and Beyond. In this election year, the Vision faces an uncertain future. The 5+ years between Shuttle retirement and a new spacecraft is a matter of deep concern. The gap may be filled by privately built spacecraft.
Bigelow Aerospace and the United Launch Alliance have been in talks to send payloads into orbit. Starting in 2011, Atlas V boosters would service Bigelow's inflatable habitats. Atlas V would be human-rated to carry a crewed spacecraft. Along with SpaceX's plans for a crewed vehicle, we may fill the gap yet.
UPDATE: Whoops, this entry didn't get posted last week as planned. In the meantime Atlantis has finally launched and docked successfully with ISS. This flight was originally scheduled for October. With all the delays in spaceflight, do they really think they will launch Orion in March 2015? NASA's new budget plans for 2015, with an expanded astrophysics plan too.