First, get remote branches up-to-date.

$ git fetch
$ git svn fetch  # only if you have Subversion remote repository using git-svn

Show remote branches.

$ git branch -a
* master
  remotes/origin/master
  remotes/svn/tags/RELEASE_20101022
  remotes/svn/tags/RELEASE_20101025
  remotes/svn/trunk

Show changes between current local branch and remote branch.

$ git diff remotes/origin/master

Show changes between current local branch and remote branch. (simple)

$ git diff --name-status remotes/origin/master

Show changes between current local branch and remote branch. (simple, Subversion repository)

$ git diff --name-status remotes/svn/trunk

Source: git svn status - showing changes that are not committed to svn - Stack Overflow