Parisian here, if you're visiting soon, you should definitely take a look around the Latin Quarter. Our museums tend to be very crowded during the tourist season, so set aside a whole day if you want to visit them. The Louvre, the Orsay and the Pompidou are the three big ones, but there are plenty of other smaller museums that are worth a shot. Read up about it on Lonely Planet, it has a pretty good section on Paris. If you're coming for a taste of our architecture, you should check out the 8th and 9th Arrondissements. The Opera, the Champs-Elysées, the Arche de Triomphe and the Boulevard Haussmann are all in this neighbourhood, and it can be a spectacular sight on a sunny day. This is also where you'll find the Galeries Lafayette, the best destination for shopping in Paris. If you want to discover French food and drink your best bet would be the 5th Arrondissement. It has plenty of good eateries and bars, and the big advantage is that it's not very touristy, so you won't risk paying too much for average food. If you want to go to one of the posher restaurants in the 1st or the 7th Arrondissements, I suggest you reserve a table right away. It can be tough to find a spot at the last minute, especially in the spring. I don't know how long you'll be staying for, but on 21 June, Paris hosts the Fête de la Musique, with loads of free concerts and stuff. It can be quite an experience. Apart from that, be sure to enjoy our parks and gardens to the fullest! The Tuileries and the Luxembourg are the two famous ones, but they are generally choc full of tourists in the spring. If you're looking for something a bit quieter, I'd suggest the Parc Monceau in the 17th Arrondissement, or the Jardin des Plantes in the 5th Arrondissement. And finally, if you are as big a Doors fan as me, don't forget to go to the Père Lachaise cemetery to pay your respects to the Lizard King! EDIT: I forgot about one thing, if you are interested in literature, you should definitely check out Shakespeare & Co., near the Nôtre Dame. It's one of the finest English bookstores in the world, with a massive selection of books, live music, book discussions and loads of other stuff! I recommend it very strongly, it's like entering into another world altogether!
Weird? Hmm. The Catacombs ? You should also see these: Parc de la Villette and this Pompidou Centre and this Maison de Verre and this Villa Savoye - probably the most significant modernist building in the world.
Never been there, have a blast lil! Have a listen to my french friend Augus. He's an extremely talented songwriter/singer that I've written to for years but have never met. We both released our first albums around the same time in the old "myspace" days and sent each other copies (maybe my first pen pal), but he doesn't speak english and I speak no french. We rely heavily upon google translator. He and his wife had a lovely daughter just a few months prior to me and my wife. Great guy, awesome musician. Enjoy your travels lil. I know you will!
I will second going to see The Catacombs. I did that and it's a really cool experience! La Musee des Arts Forains also makes for an interesting visit. sounds_sound list is very good, especially the Pompidou Centre.