There is always dry-run:

git push --dry-run

It will do everything except for the actually sending of the data.

If you want a more graphical view you have a bunch of options.

Tig and the gitk script that come with git both display the current branch of your local copy and the branch of the remote or origin.

So any commits you make that are after the origin are the commits that will be pushed.

Open gitk from shell while in the branch you want to push by typing gitk&, then to see the difference between what is on the remote and what you are about to push to the remote, select your local unpushed commit and right-click on the remote and choose "Diff this -> selected":

Make sure you've staged some changes. Otherwise, git commit -v will show you a block similar to what you posted, but not do anything. You can stage changes manually with git add, or if the files are already versioned, you can use git commit -a -v to stage and commit the changes.

For example:

$ echo "more foo" >> foo.txt
$ git commit -v
# On branch master
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#   modified:   foo.txt
#
no changes added to commit (use "git add" and/or "git commit -a")

Staging the change shows the diff with git commit -v:

:: git add foo.txt
:: GIT_EDITOR=cat git commit -v

# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#   modified:   foo.txt
#
diff --git a/foo.txt b/foo.txt
index 257cc56..a521556 100644
--- a/foo.txt
+++ b/foo.txt
@@ -1 +1,2 @@
 foo
+more foo
Aborting commit due to empty commit message.

If you just want to see the diff without committing, use git diff to see unstaged changes, git diff --cached to see changes staged for commit, or git diff HEAD to see both staged and unstaged changes in your working tree.

UPDATE: given your edit, what you really want are the git diff derivatives above. I'm not sure how Aptana Studio works. It may not follow the typical command line git flow. On the command line, you'd stage your changes, and then commit. And the above git diff commands are what you'd use to examine those changes. I typically alias them as git unstaged, git staged, and git both by adding this to my ~/.gitconfig:

[alias]
    # show difference between working tree and the index
    unstaged = diff

    # show difference between the HEAD and the index
    staged = diff --cached

    # show staged and unstaged changes (what would be committed with "git commit -a")
    both = diff HEAD

Use git-diff:

git diff -- yourfile

Here you'll find your answer:

Using Git how do I find changes between local and remote

For the lazy:

1. Use "git log origin..HEAD"
2. Use "git fetch" followed by "git log HEAD..origin". You can cherry-pick individual commits using the listed commit ids.

The above assumes, of course, that "origin" is the name of your remote tracking branch (which it is if you've used clone with default options).

git show

will show the details of the commit last commit.

If there were more than one commit you can also use

git diff origin/master

assuming your remote is named origin and the branch you want to push to is master.

As mentioned in "Shorthand for diff of git commit with its parent?", you can also use git diff with:

git diff COMMIT^!

or

git diff-tree -p COMMIT

With git show, you would need (in order to focus on diff alone) to do:

git show --color --pretty=format:%b COMMIT

The COMMIT parameter is a commit-ish:

A commit object or an object that can be recursively dereferenced to a commit object. The following are all commit-ishes: a commit object, a tag object that points to a commit object, a tag object that points to a tag object that points to a commit object, etc.

See gitrevision "SPECIFYING REVISIONS" to reference a commit-ish.
See also "What does tree-ish mean in Git?".