Tagbar
Vim plugin that displays tags in a window
...This gives you at-a-glance insight into the layout of large source files, which is especially useful for navigating unfamiliar codebases or when working on complex modules. The Tagbar sidebar also allows direct navigation: you can click on or jump to specific tags from the list, which makes it much faster to move between definitions than manually searching. Because it uses an external tags generation tool, the plugin can support many languages (C++, Java, Python, etc) with varying degrees of induction based on the tags file. Many users report that Tagbar significantly reduces the time they spend hunting for definitions.