File Type Mechanic is a nice program that can scan for missing files or file associations. The program comes with a database of file types. It knows which of your programs can open a particular file. Scan results are given to you as lists of file types with problems and can automatically be repaired if compatible programs are found installed on your computer.
File Type Assistant can help you open files with unknown extensions. The program integrates with your system and automatically displays a window when an unknown file type is found. Thus, using the program is really easy because choosing the desired option from a menu is all it takes.