It is important to use a bug tracking system to maintain a list of bugs and issues that need to be fixed in your code, and of features that you'd like to work on. Sometimes, a simple file kept inside the version control system would be enough, but at other times, you should opt for a web-based bug tracker.
For more information, see:
“Bug Trackers” list on Shlomi Fish’s “Software Construction and Management Tools” page.