When I work on someone else's code, I tipically need to abuse of grep in order to find data types declarations etc, and this usually makes me confused.
I'd like to have some tool which analyzes the source code and produces some graphviz-like drawing and allows me to follow dependencies.
Also I've found this on the internet, but I think is taylored for the linux kernel only.
Have you tried doxygen?
Doxygen can produce dot files, and you can build the docomentation without changing the source code with the right options set in the Doxyfile.
Do you use an editor that can take advantage of tags ? In Emacs, I just type M-. to go to the definition of a symbol, and M-* to go back to where I was once I have read it. This also enables the command tags-search to grep among the files of the software project (very convenient if they are in multiple directories).