Improvements:

    Changed Slider's div id from container to slider,
    made more sense to me

    This forward my attention to the css file.

    jQuery have each loops:
    $('#slider').each(function(){..
    One of the uses of this loop is making a wrapper for your
    functionality.

    var $self = $(this);
    this line is for handling problems with child scopes.
    hmm here is an example of child scope problem -

    $('#slider').each(function(){
        // $(this) - $('#slider')
        var $self = $(this);

        $self.find("#next").click(function() {
            // $(this) - $self.find("#next")
            $self.find('> img:visible').css('display', 'none')
                 .next('img').css('display', 'block');
        });
    });