MRU - Most Recently Used Files in a split
Tcomment - Fast and Easy commenting
Snipmate - Textmate like snippets, eg: type div press tab, it'll auto complete to HTML Div Element.
Sparkup - It makes HTML Coding Super Fast, Very useful for creating Nested Tags.
Surround - To Quickly Add delete, Braces, parenthesis, quotes etc.
Relative Line Numbers - To toggle relative line number mode through ctrl+l
Colorschemes I like: Jellybeans and Solarized
- 'NERD_tree': provides a hierarchical directory view in a sidebar (much like a project view); open a file by hitting enter, or by double-clicking in MacVim
- 'a': toggle quickly between a source file and its header
- 'cscope_maps': search through my cscope-indexed source files and system headers
- 'fuf' and 'l9' (a.k.a. FuzzyFinder): quick way to open files, auto-completing as you type
- 'tagbar': displays navigable list of functions/methods in a sidebar (better than the old 'taglist' plugin)
Syntastic: calls out syntax errors for lots of different languages.
Command-T: I've had some trouble getting this compiled and keeping it working when updating vim. But it's the how I open new buffers.
Solarized: is a nice :color. I use the dark.
Pathogen: seems to be the way to manage plugins. I started vim from textmate ~a month ago using Janus. This week I changed from Janus to pathogen and it's a lot nicer now. (all of tpope's stuff is great as zefhous us mentioned.)
They are all so great, but I will list a bunch that you should check out anyway: fugitive, unimpaired, pathogen, ragtag, surround, endwise, repeat.