There's lots of really great information out there about Vim but here are a couple of the extensions and resources that I use the most.
Being able to decrypt and encrypt files from within Vim is incredibly useful. The great part about this extension is that it will detect the file type and then prompt you for the decryption automatically. See the gnupg.vim information on vim.org for more detail.
SPF13-vim is a really nice distribution of vim with a lot of the common plugins included. Even if you don't want to use it directly there are lots of good ideas here.