Should be possible using any hex viewer. Some of the apps I have used which can do the same are (assuming you are asking for the Windows platform) -
* Ultra-Edit 32 (Multipurpose text editor)
* DOS debug command (you may not be able to view file contents unless it is loaded in memory and you know the offset in memory where it is stored)
* Irfan View (Freeware graphics viewer which can display a file in Hex mode with the ASCII representation alongside).
- LF