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.
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.