Django form field on the basis of jQuery plugin Tag-It! http://aehlke.github.com/tag-it/

forms.py

class TagitWidget(forms.HiddenInput):
    """ Widget on the basis of Tag-It! http://aehlke.github.com/tag-it/"""

    class Media:
        js = (settings.STATIC_URL + 'js/tag-it.js',
              settings.STATIC_URL + 'js/tagit_widget.js',)
        css = {"all": (settings.STATIC_URL + 'css/jquery.tagit.css',)}


class TagitField(forms.Field):
    """ Tag field """

    widget = TagitWidget

    def __init__(self, tag_model, *args, **kwargs):
        self.tag_model = tag_model
        super(TagitField, self).__init__(*args, **kwargs)

    def to_python(self, value):
        tag_strings = value.split(',')
        return [self.tag_model.get_or_create(tag_string) for tag_string in tag_strings if len(tag_string) > 0]

    def validate(self, value):
        if len(value) == 0 and self.required:
            raise ValidationError(self.error_messages['required'])

    def prepare_value(self, value):
        if value is not None and hasattr(value, '__iter__'):
            return ','.join((unicode(tag) for tag in value))
        return value

    def widget_attrs(self, widget):
        res = super(TagitField, self).widget_attrs(widget) or {}
        res["class"] = "tagit"
        return res

models.py

class Tag(models.Model):
    """ Model of Tags """

    name = models.CharField(max_length=200, null=False, verbose_name="Tag name")
    slug = models.CharField(max_length=400,
                            editable=False,
                            verbose_name=u'Slug',
                            unique=True,
                            null=False)

    def __unicode__(self):
        return self.name

    @staticmethod
    def _generate_slug(value):
        slug = ''.join(ch for ch in value[:200] if category(ch)[0] != 'P')
        return urlquote(re.sub(r'([ ]+_)|(_[ ]+)|([ ]+)', '_', slug))

    def save(self, *args, **kwargs):
        self.name = self.name.lower()
        self.slug = self._generate_slug(self.name)
        super(Tag, self).save(*args, **kwargs)

    @classmethod
    def get_or_create(cls, value):
        slug = cls._generate_slug(value.lower().strip())
        if cls.objects.filter(slug=slug).exists():
            return cls.objects.get(slug=slug)
        else:
            return cls.objects.create(name=value.lower().strip())

tagit_widget.js

$(document).ready(function() {
    $(".tagit").tagit({
		allowSpaces: true,
		autocomplete: {
			delay: 0,
			minLength: 2,
			source: "/tag_autocomplete/"
		}
	});
});

views.py

@login_required
def tag_autocomplete(request):
    """ url: /tag_autocomplete/"""
    
    if not request.is_ajax():
        raise Http404

    value = request.GET['term']

    available_tags = Tag.objects.filter(name__startswith=value.lower())

    response = HttpResponse(json.dumps([unicode(tag) for tag in available_tags]))
    return response