HxD is a hex editor capable not only of open files, but also one which can read and write data to hard disk sectors and processes in memory. A review of HxD has also been published.
Download HxD 1.7.7.0 (from Programming Tools)
disk editor, disk images, fast, hexeditor, huge files, large files, memory editor, ram editor, simple, hex editor0.83 MB | For Windows 7, Windows 8 (64-bit, 32-bit) / Vista / XP | Free