Smart code-completion for Vim, including C/C++ support via libclang. As a bonus, it also integrates well with Syntastic (syntax checking plugin for Vim that also integrates with Clang). Takes a little bit of work to set up the first time (need to compile a helper-library and each project needs compiler flags set), but I found that works pretty well with CMake/Clang's compilation database support (allowing YouCompleteMe and Syntastic to use CMake's compile flags).