Formula Navigator

From Spreadsheet Guys:

Formula Navigator is a clever tool for understanding the linkages within a complex spreadsheet. It is both a spreadsheet productivity enhancer and spreadsheet review tool, useful for anyone working with large and complex Microsoft Excel spreadsheets on a regular basis. Formula Navigator allows you to navigate through complex multi-sheet Microsoft Excel workbooks with ease. It facilitates simple navigation to all known precedents or dependents using a list of dynamic hyperlinks regardless of whether they are on another worksheet or in another open workbook. Formula navigator has a unique floating window, which has the convenience of always being on-top, to have the display constantly at your fingertips - as well as functionality to minimize and/or resize the window to keep it out of the way when screen real-estate is of high importance. Your navigation history is maintained allowing you to jump back to sections of the workbook which you were previously looking at.