WinHex Hex Editor

• This is the most powerful shareware in the planet for Hex editing, you can edit files, memory and whole disk partitions, you can recover missed files or folders
• Disadvantages: after we tested this software to recover some files, faild to recover them..at the same time other recovery softwares succeeded to recover them..
  
• These are some key features from product's webpage:

1. Disk editor for hard disks, floppy disks, CD-ROM & DVD, ZIP, Smart Media, Compact Flash, ...
2. Native support for FAT, NTFS, Ext2/3, ReiserFS, Reiser4, UFS, CDFS, UDF
3. Built-in interpretation of RAID systems and dynamic disks
4. Various data recovery techniques
5. RAM editor, providing access to physical RAM and other processes' virtual memory
6. Data interpreter, knowing 20 data types
7. Editing data structures using templates (e.g. to repair partition table/boot sector)
8. Concatenating and splitting files, unifying and dividing odd and even bytes/words
9. Analyzing and comparing files
10. Particularly flexible search and replace functions
11. Disk cloning (under DOS with X-Ways Replica)
12. Drive images & backups (optionally compressed or split into 650 MB archives)
13. Programming interface (API) and scripting
14. 256-bit AES encryption, checksums, CRC32, hashes (MD5, SHA-1, ...)
15. Erase (wipe) confidential files securely, hard drive cleansing to protect your privacy
16. Import all clipboard formats, incl. ASCII hex values
17. Convert between binary, hex ASCII, Intel Hex, and Motorola S
18. Character sets: ANSI ASCII, IBM ASCII, EBCDIC, (Unicode)
19. Instant window switching. Printing. Random-number generator.
20. Supports files >4 GB. Very fast. Easy to use. Extensive online help. (more)

• Screen shots from Softpedia
• License: FreeToTry, between $39 and $176 to buy
  
• WebPage
• Download: you can download the latest version from its webpage.

mirke.de Tiny Hex Editor

• The most powerful tested freeware of: hex, disk, ram editings and compare files in graphical HEX environment
• You can change virual memory of any running process
• You can Read/write disk sectors, RAM and other features
  
• License: Freeware
• Screenshots from Softpedia
  
• Download Link1 *.exe
• Download Link2 *.cab
  
• Homepage

Open Source Hex Editor VB

• Hex Editor VB is an open source freeware hexadecimal editor for Windows. It allows to view and/or edit files, process memory and physical/logical disks. It includes lots of functions like file management, process management, advanced conversions between bases, disassembler...
• the source in VB6
  
• License: Freeware under GNU
  
• Operating System: 32-bit MS Windows (NT/2000/XP)
• Screenshots from SourceForge
  
• Homepage and download link