The following haven't been tested mostly because I can't figure out how to do so.
diff --minimal
diff --horizon-lines
diff --speed-large-files
diff --show-c-function
diff --show-function-line
diff --starting-file
diff -x | -X in combination with --ignore-file-name-case as the latter doesn't work due to a bug.
diff3 -a
diff3 -T