I have tried Kompare, and currently I am using Meld which is an excelent program and does most of what I want except for a few minor things.

First I guess I should explain me use case which is slightly different than normal, I do not run the diff on source code instead I run it on the files my editor sends me to see what changes where made to the text.

The problem is that meld tries to go for a character match if possible, when it probably should try to compare words. Newlines and spaces should also be treated as interchangebale, right now whenever the word wrapping changes meld treats each new space symbol where a newline used to be as a change.
Finnaly it would be nice if reordering words would be marked different than other changes.

Overall though meld works quite well, and I am using it for a purpose it probably wasn't desinged for, still there must be some call for comparing natural language documents so are there any suggestions for tools more suited to this task?