Use a bug tracking system starting tomorrow. Look at solutions like Rally or Fogbugz. ASAP. Don't let them code another release without tracking. Tie the source control system into these platforms in some fashion even if it is simply the rule that states, "No code is checked into the tree without a bug number." You do use an enterprise-class source control platform, right?
Our developers really aren't good about keeping track of all the things they change when they are working on new versions that involve not only enhancements to the product, but bug fixes, table changes, trigger changes, etc that need to be communicated to customers when they are provided a new release version.
Does anyone have any guidance about how to track and maintain this information?