Some languages make heavy use of lambdas to the point that you may like to fold them. vim-lambdify (GitHub: calebsmith / vim-lambdify) by Caleb Smith is a plugin that conceals lambdas and inline functions with a lambda character.
Plugins such as vim-haskellConceal and vim-cute-python use this to replace many different things with more pithy/mathy symbols. The approach taken here is to replace only lambdas, but to do so for many different languages to avoid having to use many plugins for a single feature.
I imagine this would look really cool in functional languages if you use the λ character.