EDIT: it can still be accessed from here https://news.ycombinator.com/bookmarklet.html
EDIT 2: the bookmarklet is also linked from HN's "submit" page, just below the form.
javascript:window.location=%22http://news.ycombinator.com/submitlink?u=%22+encodeURIComponent(document.location)+%22&t=%22+encodeURIComponent(document.title)
EDIT: it can still be accessed from here https://news.ycombinator.com/bookmarklet.html
EDIT 2: the bookmarklet is also linked from HN's "submit" page, just below the form.