For doing task management well, I found that vertex42 does make a good Excel gantt chart template. However, I can not modify that template due to I don't know the unprotect password. Hence, I make a similar one, and add some features useful to me. My simple Excel gantt chart template can be downloaded from Here (<-- download link is here~! at Google Code)
Note: If you have any modifications & suggestions, please contribute to this project, and make it better and better.