Thank you!
OK... let's see...
One thing must be said first, to avoid any disappointment: if you're hoping to find the city as seen by Brassai or Doisneau... forget it
Paris no longer has that special charm that was reeking out of their photographs, you'll find a metropole crowded with busy people and swarms of tourist (yes, there will be plenty of them, even this early in the year). I'm not saying there aren't bits and pieces left of the old city, but you'd need too much time to wander around the streets to discover them. Sad, but true.
Now...
Try to set up an 'action plan' before getting to Paris. Write down what you would like to see/visit, and spread them across the time you'll spend there. You mentioned it would be a weekend, I'm afraid that won't be enough, really, so you need to prioritize.
If you had plans to visit the Louvre, forget about it. Seeing everything they have there would take you a day at least (including the time you'll spend waiting to get in); plus, most of the interesting stuff they have there, you have already seen in pics/videos/documentaries. But do visit the museum on the outside, you'll surely have enough photo opportunities, even if you risk falling for the all-known postcard-shot, like I did
(day-time is OK, evenings are better, IMHO)
Sacre Coeur is a must, especially if you can arrive there early in the morning, before the tourists arrive (ideally, you'd want to be there just before sunrise). They won't let you take photos inside (IIRC), but the outer architecture of the church demands to be photographed, plus you'll get a wonderful vista of the city.
Also, check out the area around the church, behind and to the east of it there are some wonderful little streets that aren't packed with tourists.
In the city centre, do enter Notre-Dame, you can take pics there. And while you're in the area, walk the streets around (very nice, although crowded), and do not miss a small church called Saite-Chapelle: it has some of the most beautiful stained glass in Europe (most people ignore it, after going to Notre-Dame). North of these two churches lie Place des Vosges and Le Marais, not-to-missed, IMHO.
On the South bank, there's the Quartier Latin area, with plenty of things to see as well, the Pantheon and La Sorbonne are connected by a lot of small streets, which could give you a nice experience. Eating at the small restaurants here is cheaper and better than in the more famous places, I'd say... but if you want to try such a place, maybe look up La Closerie Des Lilas, Hemingway's favourite restaurant.
Then there's La Defense, of course, La Grande Arche and La Cheminée de Moretti spring to mind right now
I would visit this part of Paris in the afternoon, maybe even wait for the sunset around the Arch (if that doesn't mean giving up Montparnasse Tower evening).
I didn't mention the Eiffel Tower or The Triumph Arch, beacause everyone knows them, but these shouldn't be missed either. Reserve an afternoon for them, maybe a long walk like... L'Arc De Triomphe - La Tour Eiffel - Ecole Militaire - Hotel Des Invalides - Champs Elysees - Jardin Des Tuileries to end up at the Louvre in the evening?
Bois de Boulogne didn't do much for me, perhaps it is nicer in autumn, but in spring... there's no point in waisting your time there.
The Catacombs... only if you insist on visiting, but you'll need at least an F2 lens to shoot there handheld (and it's rather difficult to set up a tripod, with all those tourists). Same goes for the cemeteries (Montparnasse, Pere-Lachaise), unless you must say hello to Jim Morrisson, of course
I know it's a long list so far, but if you'll have any time left, maybe you'd enjoy a walk along Canal Saint Martin. This is something we planned to do, but later found out we ran out of time, mostly because of the lack of proper planning. Again, I must stress out the importance of careful planning! My biggest regret about our Paris holiday was never making it to a meeting with a fellow photographer, a Parisian whom I had met on a Minolta forum (again, because of less-than-wonderful planning).
Oh... he's shooting Pentax too, now, btw
I almost forgot. There's a website with quite a few tour suggestions around Paris, you might find it useful (sorry, I can't seem to find a link for the English version, just French):
Promenades dans le Paris Insolite - Promenades Paris Inconnu - Paris Insolite
Check out at least Parcours 2 - Vieux Paris, if possible.
Well.. that's about it for now. If I can remember something else, I'll come back