I regularly use PC Study Bible for lesson preparation and studying, and find it very valuable. I know Craig uses Logos (someday I'll have to get him to show me how to get more out of it). There are a couple of other major competing commercial packages out there that are undoubtedly good too, and quite a few sites now that have multiple Bibles and other resources that can be searched. I've just been looking at e-sword which is available as a free download (Windows systems) and has several versions and aids available for it. It has some interesting features, and at first glance I like it.