Reading STDIN

This is pretty basic, but it's also really useful. Vim can read standard input via a pipe at the end of any common command chain. I use Vim in conjunction with diff all the time to analyze the difference between two or more source files.

diff -u Scheduler.old.java Scheduler.java | vim -

Compare the difference of two source trees before submitting your patch:

diff -Naur oldtree newtree | vim -