Is there a module that creates a jquery-like bar that displays system messages at the top of the page. (exactly like the large, red bar on this site (stack exchange)?
You could have a look at the "Purr Messages" module - I haven't used this myself, so I don't know if it allows for the messages being displayed at the top - it says it creates a "jquery popup," which I suppose means an absolutely positioned div which either fades out or you can click away with your mouse.
I did something similar to this this on one site by simply editing
page.tpl.php - but it sounds like you want a module, & not coding advice.
You can also check out the Absolute Messages module. I have used it many times. Here is a quote about it (from the module's project page):
Displays system messages in fully themeable colored horizontal bars on top of the page, similar to Stack Overflow / Stack Exchange network notifications.
- when messages are displayed content is pushed down respectively, so that nothing is covered and everything could be still interacted with,
- alternatively, messages could be fixed to the top of the browser's viewport, so they will always remain visible regardless of scrolling,
- each message has its own "Dismiss" (close) icon,
- optional "Dismiss all" icon is displayed if total number of messages exceeds value defined in module settings,
- messages could be dismissed automatically after a specific time - configurable in module settings for each message type separately,
- hovering mouse cursor over messages resets dismiss timer,
- provides option to re-show all already dismissed messages,
- provides option to display only first n lines of each message, with remaining part shown after clicking on the message,
- provides separate permissions to administer and to access Absolute messages,
- full control over output with template files,
- uses standard jQuery library without other modules or plugins dependencies,
- falls back to standard Drupal's way of displaying messages when JS is not available (or when user does not have access absolute messages permission granted),
- provides option to skip "has_js" cookie checking, which disables fallback to standard Drupal messages if no JS has been detected (for example in case of Pressflow, which dropped "has_js" cookie completely),
- displays devel messages as standard Drupal messages.