TJ’s Site News allows you to display a message on every page. Customisable message that allows html and can be turned on or off.
AnswerTips are small bubbles of information triggered by double-clicking any word on an AnswerTips-enabled page that allows your visitors to access definitions and fast facts on millions of obscure words, personalities or slang.
MarketingTrick is a plugin that gives access to full text of posts only to registered users, but has some additional functionalities than just to force users to register/login.
StickPost allows you to stick a post to the top of the homepage.