Each of these walking tours is designed to be around 3 hours in length, at a casual stroll, giving you time to admire the sites, window shop, etc. 

Left Bank - Latin Quarter/East
Left Bank - Montparnasse/Luxembourg
Left Bank - Latin Quarter/West
Left Bank - Rodin/Les Invalides
Left Bank - Ile de la Cite & Ile St Louis
Right Bank - Montmartre/Sacre Coeur
Right Bank - Champs Elysees
Right Bank - Louvre/Shopping
Right Bank - Les Halles/Le Marais
Right Bank - Opera/
 

Many of these attractions are noted in the walking tours, and can either be combined with a tour, or visited separately as a specific destination.

If there is an official web site, I include the link.

The rating system is based on my experience visiting the site, it's overall historical significance, ease of access, and where it falls into the "must see if I go" category.  Where appropriate, I will also note if tours are available in English, and any other pertinent data I happen to come across.

Must see
Probably Shouldn't Miss
Most people like it
Pretty Cool
If you have time 

La Conciergerie
One of the oldest French prisons, built primarily in the 14th Century.  Tours offered in English.  This is where Marie Antoinette was held prisoner until she was beheaded.
Open 9h30 to 18h30 from 1 April thur 30 September and from 10h00 until 17h00 from 1 October thru 31 March
Entry fee is €5.50

Le Basilique de St. Denis
This cathedral was built on the ground where the decapitated St. Denis was said to have taken his final breath after he made his long run from Montmartre holding his head in his hands.  It is now a monument to the resting place of Kings and Queens of France dating back to Hugh Capet.  Although it was virtually decimated during the revolution, Violet le Duc (who restored Notre Dame de Paris) did an outstanding job of restoring it to what it may have looked like when the last Kings and Queens were buried there.  Tours are available in English via an audio guide.
Metro: Basilique de Saint-Denis
Open 10h00 to 17h15 in the summer and 10h00 until 18h15 in the winter except that it's closed on Sunday mornings until noon.
Entree fee: 6,10€

Notre Dame de Paris
There is not much I can say about this place as it's such a well known landmark that guide upon guide has been written about it.  I think you can get a lot more out of your visit if you do your homework on Cathedral's before you go.  Although a guided tour is not necessary to enjoy the beauty of the Cathedral, it can be most fascinating to learn some of the special points of interest about the site.  Look for the headless figure of St. Denis on the left front portal, and note that the statues above the front portals reconstructed by Violet le Duc are not what they used to be.  Thought to be Kings and Queens during the revolution, their heads were destroyed, but later found, and can now be seen at the Musee de Cluny.

Ile de la Cite Archeological Dig
Located just in front of Notre Dame with the entrance down a few stairs facing east, this is a great way to spend a few hours marveling at an archeological dig uncovered during renovations for a parking garage.

Point Zero
Just look for the group of tourists out front of Notre Dame looking at the ground, and you've found Point Zero.  It is from this point that all distances in France are measured to Paris
 

Montmartre
Le Sacre Coeur
The Sacre Coeur is an absolute must for all visitors in my opinion.  While the basilica itself provides for some eye-popping oohs and aahs, it is the Sacre Coeur's location that truly makes it spectacular.  Perched high atop the Butte Montmartre, it overlooks all of Paris.  The steps leading up to the basilica from the bottom of the hill are generally cluttered with a multitude of people, both local and visitors.  On a warm summer day, you will find singers, jugglers, and actors all with a hat to pass.  The view of the surrounding area is unparalleled anywhere in Paris.  A climb to the top of the dome (Visite du Dome) will afford you a 360° view of the entire city, and an up close and personal view of the various gargoyles located around the dome.  There are very few places in Paris where you will catch your breath in awe as many times as you will at the Sacre Coeur. 

Note:  If you plan to take the Visite du Dome, you will find the entrance on the left side of the basilica (facing the front), and down a few steps.  There is a gift shop on the left side of the main church which can give you directions.  There are a few hundred winding stairs to the top, that are in places, impassable by two persons at once.  You will also walk inside the basilica's dome to gaze down into the church, and across the roof.  If you have any fear of heights, I don't recommend doing this.

Place du Tertre
The Place du Tertre is located just to the east of the Sacre Coeur.  It is a lively square that is frequented by a number of tourists, but you will also find plenty of local Parisians stopping by.  Several restaurants line the square, and it's a great place to have lunch on a warm day to people watch.  The square itself is filled with artists who do everything from sell their wares to create instant portraits, cutouts and caricatures.  Food at most of the restaurants is good, but not great.  If you eat here, do it for the atmosphere, not for the food.  It's not so expensive as you might think to eat, however, beware if you sit down just to have a coffee or beer.  These restaurants have devised a unique way of getting around the old French custom of letting you keep your table as long as you want even if you just buy a coffee.  Alas, here you can dine on Steak Frites for $10, but un cafe will cost you $8!!  The have very few customers who sit for coffee.

Les Vignes de Montmartre

Le Moulin Rouge

Adult Stores

Les Invalides
Museum/Napoleon's Tomb

Son et Lumiere

La Tour Eiffel

Statue de la Liberte

Palais de Chaillot
 

Paris Catacombs

Cemeteries
Montparnasse
Pere Lachaise
Montmartre

L'Arc de Triomphe

Champs Elysees

The Old Opera House

The New Opera House (Bastille)

Ste. Chapelle
 

It is very difficult to plan your day when including any of the museums found in Paris, because it's hard to determine just how much time you want to spend in each place.  2-3 days in the Louvre alone may not be enough, depending on what your plans are.  However, you can certainly see all of the highlights in a half day tour.  Best advice is to give yourself time limits, decide what you want to see before you arrive, and plan your visit around those specific works.

If you plan to see a number of museums, you may want to consider purchasing a Museum and Monument Pass.  Available at virtually all major Metro stations, the pass offers unlimited and immediate access to over 70 museums and monuments around the city and in the Ile de France.  It is available in 1, 3, & 5 day passes.  For more information and rates, you can visit the transportation authority's website at www.ratp.fr and click on the British flag for their English version.  Then click on Museum & Monument Pass.  This pass, in French called the Carte Musee et Monuments, includes the following sites:

In Paris...

l'Arc de Triomphe
Musee de l'Armee
Centre Pompidou - Modern Art Museum
Porte Doree Tropical Aquarium
Musee des Arts decoratifs
Musee des Arts et Metiers
Musee national des Arts et Traditions populaires
Musee de l'Assistance Publique - Hopitaux de Paris
Chapelle expiatoire
Cite des Sciences et de l'Industrie
Conciergerie
Musee national Eugene Delacroix
Musee de Egouts de Paris
Musee Galliera - Musee de la Mode de la Ville de Paris
Musee Hebert
Musee Jean-Jacques Henner
Musee de l'Institut de monde arabe
Musee du Louvre
Musee national de la Marine
Musee de la Mode et du Textile
Musee de la Monnaie
Musee Gustave Moreau
Musee national du Moyen Age - Thermes de Cluny
Musee de la Musique
Musee Nissim de Camondo
Crypte archeologique du Parvis de Notre-Dame
Tours de Notre-Dame
Musee de l'Ordre de la Liberation
Musee d'Orsay
Pantheon
Nusee national Picasso
Musee des Plans-reliefs
Musee de la Poste
Musee de la Publicite
Musee Rodin
Sainte-Chapelle

Sites around Paris...

Musee de l'Air et de l'Espace
Musee des Antiquites nationales de Saint-Germain-en_Laye
Musee national de Ceramique de Sevres
Abbaye royal de Chaalis - Musee Jacquemart-Andre
Chateau de Champs
Musee national du Chateau de Compiegne
Musee Conde - Chateau de Chantilly
Musee national de la Cooperation franco-americaine - Chateau de Blerancourt
Musee departemental Maurice Denis - Le Prieure
Musee national du Cheateu de Fontainebleau
Musee national de Granges de Port-Royal
Cheteau de Maisons-Laffitte
Musee national des chateaux de Malmaison et Bois-Preau
Chateau de la Motte Tilly
Chateau de Pierrefonds
Chateau de Rambouillet
Musee national de la Renaissance Chateau d'Ecouen
Maison d'Auguste Rodin a Meudon
Basilique Saint-Denis
Villa Savoye
Musee national des chateaux de Versailles et de Trianon
Chateau de Vincennes