Sam's Club introduced some new changes today:
Looks like they got rid of the business membership (boo!) and are really pushing the Plus membership by now including free shipping online on most items with a Plus membership (and reducing the number of items that include free shipping for non-Plus members).
Without the business membership, the only way to get the early shopping hours Monday-Saturday is with the $100 Plus membership.
Whichever card you have, you can add additional people to your account for $40 each, but those people will be considered non-Plus members.