I ran into a merge conflict. How can I abort the merge?

Since your pull was unsuccessful then HEAD (not HEAD^) is the last "valid" commit on your branch:

git reset --hard HEAD

The other piece you want is to let their changes over-ride your changes.

Older versions of git allowed you to use the "theirs" merge strategy:

git pull --strategy=theirs remote_branch

But this has since been removed, as explained in this message by Junio Hamano (the Git maintainer). As noted in the link, instead you would do this:

git fetch origingit reset --hard origin

If your git version is >= 1.6.1, you can use git reset --merge.

Also, as @Michael Johnson mentions, if your git version is >= 1.7.4, you can also use git merge --abort.

As always, make sure you have no uncommitted changes before you start a merge.

From the git merge man page

git merge --abort is equivalent to git reset --merge when MERGE_HEAD is present.

MERGE_HEAD is present when a merge is in progress.

Also, regarding uncommitted changes when starting a merge:

If you have changes you don't want to commit before starting a merge, just git stash them before the merge and git stash pop after finishing the merge or aborting it.

git merge --abort

Abort the current conflict resolution process, and try to reconstruct the pre-merge state.

If there were uncommitted worktree changes present when the merge started, git merge --abort will in some cases be unable to reconstruct these changes. It is therefore recommended to always commit or stash your changes before running git merge.

git merge --abort is equivalent to git reset --merge when MERGE_HEAD is present.

http://www.git-scm.com/docs/git-merge