My favorite one was "HxD" as it is neat and easy to use. It has limited functions but enough most of the time.
Besides i tested some others (see list below, please contribute!):
- FlexHEX (Finde keinen Compare)
- HexCmp => More a compare tool than an editor, but it does it's job very well! This is not Freeware. Can compare two files
- Hex Workshop v6.8 => REALLY good tool! Unfortunately the compare function does not highlight the diffs, you need to "step through" them.
- VBinDiff => old NC-style DOS ANSI-Graphics tool for the commandline only. Forgett it...
- XVI32 => Totally nonsense, void this