This list will be periodically updated over the course of what is likely to be a busy 2015 season. The Astros will be trying to position themselves for contention, and 2015 likely represents the last chance for some long-ish tenured Astros. I may have missed someone - please feel free to discuss and mention below in the comments.
Since the end of the 2014 regular season, the Astros have seen the following players enter or exit the organisation. Some of the exits remain with the organisation, but are considered exits because they were outrighted off the 40-man.
Enter:
Angel Baez, P, Mar 2015.