I think only permanent objects should be considered, so no flares. For that matter, the ISS is fairly ephemeral but I think its fair enough to include it.
Including ISS is arguable. It originated from earth, and so is not really 'extraterrestrial', plus, technically, it's low earth orbit is still within the earth's atmosphere.
I used to know well the names of Vega, Arcturus, Procyon, etc... some of them featured in fan-fiction authored by myself or my girlfriend in high school. We were both sci-fi geeks. And I studied Astronomy once a long time ago. Now, 20 years later, I only could remember 3 stars, but I got all the other objects.
Are Halley's and other comets not brighter than some of these stars? Do these objects have to be visible from Earth at all times? I would think not since it is based on maximal brightness not averages. Though... then you open up the possibility of objects entering the atmosphere. I bet the asteroid that wiped out the dinosaurs was pretty damn bright for at least a short while.
Right now it does - when it gets to the inner solar system its magnitude is lower than 6, making it a great comet. The brightest comets ever, though, have gotten all the way to -10 (Comet Ikeya-Seki).
Definitely some more guidance needed here. I realize you can't do anything about long-period comets, but Halley's should be on there. And many of the meteor showers (e.g. Perseids) reach negative magnitudes regularly.
I've added it at -4 as that's what it says http://en.wikipedia.org/wiki/International_Space_Station
although it can reach -5.9 according to http://en.wikipedia.org/wiki/Apparent_magnitude