Ubuntu Mono fonts patched for the "Powerline" vim plugin: https://github.com/Lokaltog/vim-powerline/
Assuming you already installed and configured vim-powerline,
if you're using Ubuntu (or some similarly .font-configured linux variant), then all you need to
do is:
cd ~/.fonts/ && git clone https://github.com/scotu/ubuntu-mono-powerline.git && cd ~
If you're using something else, like OSX, then you'll need to download these and install them the usual way.