There isn't a direct replacement for the Share button of old. WIth Open Graph, Facebook gives you (the site owner) the power to describe your pages and have more control over what a user's feed post about your page will look like. You can set the title, description, and image that are used when a user clicks the Like button. For the user, when they click the Like button, they get a comment box popup and a "Post to Wall" button where they can add their own comment and choose to post the Like on their wall.
The closest thing available now is a different type of popup for posting to a user's feed, which you can see below:
developers.facebook.com/docs/reference/dialogs/feed/
With that, you (the admin) still have to specify the title, description, and image that are used. The user still has the option to add a comment and click a button to post to their wall. There is no method to select an image though. Additionally, since that's not using the 'Like' button, there is no counter of popularity of that page. It's a one-time use share, whereas the Like button can draw more users in by having a higher Like count.
Hope that explains. Of course if you have any questions, just let us know.
Thanks,
Alex