public interface IUserTagService
{
    IList<string> GetUserTags();
}

@inject IUserTagService userTagService;

<script>
$(function() {
    var availableTags = @Json.Serialize(userTagService.GetUserTags());
    $("#tags").autocomplete({
        source: availableTags
    });
});
</script>

$(function () {

    $.getJSON("@Url.Action("GetItems")", function (json) {
        $( "#tags" ).autocomplete({
            source: json
        });
    });

})

public JsonResult GetItems()
{
    var list = new List<string>() {"ActionScript","AppleScript"};
    return new JsonResult(list);
}