Thinking of moving from TextMate to vim for Rails dev. What do I need?

Question

I do Ruby on Rails development pretty much exclusively. I currently develop in OS X using TextMate. I have a virtual machine running to emulate as closely as possible the enviro

Answer 1

All of the other answers plus:

Ability to have a (preferably) collapsible project tree visible either at all times or easily toggle-able.

• The project.vim plugin doesn't really work like TextMate's Project drawer but it's close.
• With NERDTree, you can setup bookmarks and make it work a little like a project drawer.
• :help mkview and :help mksession can help, too.

Ability to see SCM status at a glance, either within this project tree (preferable) or otherwise. (I use git almost exclusively if this makes any difference.)

• vcscommand.vim provides the same set of commands for multiple SCMs, it works with Git, SVN, Mercurial…
• You can use the aforementioned fugitive plugin to display the Git status in the status line, :help fugitive-statusline.

Being able to view a side-by-side diff from within vim would be great too

• fugitive provides the :Gdiff command that does just that.
• A recently released plugin called Gitv tries to emulate GitK in Vim. I like it a lot and the author is very responsive. In the tree view, hit to open a previous commit in another window and D to see a double diff.

Code completion, if possible

• There are a few solutions, if you don't need it to be automatic , and will be more than enough, if you want "autocompletion" you may try these few plugins. My favorite is autocomplpop.