ccglue is a complementary tool to cscope and ctags. The tool builds a cross-reference symbol database from cscope (and ctags) databases that can be used to display dependency-graphs (aka call-trees, code flow). Visualization can be done with the Vim CCTree plugin or the built-in stand-alone command-line tracer.
CCTree is a Vim 7 plugin that displays hierarchical call-trees for functions or files using a cscope database. The functionality is similar to that offered by other IDEs and source-analysis applications, like Kscope, Source Navigator, and Eclipse. CCTree features a symbol dependency tree analyzer for C using a cscope database. It has basic support for functions and macros, and extended support for global variables, macros, enums, and typedefs.