Move the most recent commit(s) to a new branch with Git

Moving to an existing branch

If you want to move your commits to an existing branch, it will look like this:

git checkout existingbranch
git merge master
git checkout master
git reset --hard HEAD~3 # Go back 3 commits. You *will* lose uncommitted work.
git checkout existingbranch

You can store uncommitted edits to your stash before doing this, using git stash. Once complete, you can retrieve the stashed uncommitted edits with git stash pop

Moving to a new branch

WARNING: This method works because you are creating a new branch with the first command: git branch newbranch. If you want to move commits to an existing branch you need to merge your changes into the existing branch before executing git reset --hard HEAD~3 (see Moving to an existing branch above). If you don't merge your changes first, they will be lost.

Unless there are other circumstances involved, this can be easily done by branching and rolling back.

# Note: Any changes not committed will be lost.
git branch newbranch      # Create a new branch, saving the desired commits
git reset --hard HEAD~3   # Move master back by 3 commits (Make sure you know how many commits you need to go back)
git checkout newbranch    # Go to the new branch that still has the desired commits

But do make sure how many commits to go back. Alternatively, you can instead of HEAD~3, simply provide the hash of the commit (or the reference like origin/master) you want to "revert back to" on the master (/current) branch, e.g:

git reset --hard a1b2c3d4

*1 You will only be "losing" commits from the master branch, but don't worry, you'll have those commits in newbranch!

WARNING: With Git version 2.0 and later, if you later git rebase the new branch upon the original (master) branch, you may need an explicit --no-fork-point option during the rebase to avoid losing the carried-over commits. Having branch.autosetuprebase always set makes this more likely. See John Mellor's answer for details.

For those wondering why it works (as I was at first):

You want to go back to C, and move D and E to the new branch. Here's what it looks like at first:

A-B-C-D-E (HEAD)
        ↑
      master

After git branch newBranch:

    newBranch
        ↓
A-B-C-D-E (HEAD)
        ↑
      master

After git reset --hard HEAD~2:

    newBranch
        ↓
A-B-C-D-E (HEAD)
    ↑
  master

Since a branch is just a pointer, master pointed to the last commit. When you made newBranch, you simply made a new pointer to the last commit. Then using git reset you moved the master pointer back two commits. But since you didn't move newBranch, it still points to the commit it originally did.

In General...

The method exposed by sykora is the best option in this case. But sometimes is not the easiest and it's not a general method. For a general method use git cherry-pick:

To achieve what OP wants, its a 2-step process:

Step 1 - Note which commits from master you want on a newbranch

Execute

git checkout master
git log

Note the hashes of (say 3) commits you want on newbranch. Here I shall use:
C commit: 9aa1233
D commit: 453ac3d
E commit: 612ecb3

Note: You can use the first seven characters or the whole commit hash

Step 2 - Put them on the newbranch

git checkout newbranch
git cherry-pick 612ecb3
git cherry-pick 453ac3d
git cherry-pick 9aa1233

OR (on Git 1.7.2+, use ranges)

git checkout newbranch
git cherry-pick 612ecb3~1..9aa1233

git cherry-pick applies those three commits to newbranch.