I use colordiff, and sometimes vimdiff, for some tasks.
I also like trac's character-wise diff within lines.
A command-line tool for that would be nice, does one
exist? It probably wouldn't be hard, the tricky bits
are already on CPAN (Algorithm::Diff,
hidiff was intended to show a file, but with it's
differences to another highlighted. I think there's
room to use Algorithm::Diff to improve how it does that.
I need to work out what diff information to display
and how, given the constraint that the "new" file
is shown in it's entirety and correctly positioned.
(While writing this I thought that flipping interactively
from new to old may help, or be useful on it's own)
I also just discovered "less -r" and "less -R", which
make less display colordiff output usefully.