If your Vim is not compiled with clipboards, you wish to copy selected text instead of entire lines, you do not want to install MacVim or other GUI, the simplest solution is to add this line to your .vimrc:
map <C-c> y:e ~/clipsongzboard<CR>P:w !pbcopy<CR><CR>:bdelete!<CR>
To use it, simply visually select the text you want to copy, and then Control-C. If you want a full explanation of this line read "How to Copy to clipboard on vim".