<p>Any good suggestions? Input will be the name of a header file and output should be a list (preferably a tree) of all files including it directly or indirectly.</p>

For a heavy weight solution, you should check out
doxygen
.  It scans through your code base and comes up with a website, effectively, that documents your code.  One of the many things it shows is include trees.
If you were looking to be able to plug the output of this tool into some other process, then this may not work for you (although doxygen does output to other formats, I'm not real familiar with that feature).  If you simply want to eyeball the dependencies, though, it should work great.