A simple one that works out of the box (I think) with vim is ctags, install it and run "ctags -R" in the code directory. Then in vim hit "ctrl-]" when your over

A simple one that works out of the box (I think) with vim is ctags, install it and run "ctags -R" in the code directory. Then in vim hit "ctrl-]" when your over a name to jump to it, hit "ctrl-o" take you back up a level. It's not as sophisticated as an IDE, but it works with practically any language and is easy to customize.