Far too many. Some I'm using maybe every twentieth time I start vim, but whenever I throw them out I suddenly need them...
vim-easymotion - Jump to positions easily (I still use the mouse too often)
vim-powerline - Prettier and more customizable display of useful data and the mode we're in
vim-supertab - Still fails me too often but I'm having it set to omnicomplete most of the time
minibufexpl - Old but I don't like the way the tabs works
ctrlp - Good fuzzy finder. Not sure if it's the best, but it doesn't require compiling Ruby extensions and weird crap
Gundo - Tames the undo tree
ack.vim - Integrates ack to search in files more easily
vim-css-color - Love this one. Underlays color values with the actual color
And other stuff like syntax for YAML, Jinja2 and HTML5.