2 Days in Paris

Boat trip on the Seine at night, visit Notre Dame then walk to holocaust memorial, sidewalk cafe breakfast, picnic lunch under eiffel tower & walk everywhere.

Depends on your interests: if art, the D'Orsay Museum is more manageable than the Louvre and has a wonderful lunch in its restaurant. If churches, St. Chapelle is not to be missed--the stained glass windows both downstairs and especially upstairs are magnificent. Where are you staying? What days of the week? Just walking and looking is wonderful. If you are near a market during your stay, that is worth a visit. (Different markets in different places, different days.) You will love it and you will want to go back for a longer stay.

It's difficult to advise since your interests will be different from mine. Purchase a few guide books. I use Frommer's, Steve's; DK, and Lonely Planet. Ecah will give you a different perspective on the same sights.

A stop at Angelina's for hot chocolate is a must. It is the most amazing ever. 226 rue de Rivoli near the Tuileries. You can even buy some to bring home as gifts or for yourself. Also, breakfast at Les Deux Magots (St Germain des Pres). Oh so French. Hot chocolate is great there too.
Try to fit in one of the amazing museums D'Orsay, Louvre or Centre Pompidou)depending on your taste in art.
If the weather is bad, you can always shop at Galeries Lafayette. You can lose many hours here.

Notre Dame (must climb the tower for the spectacular views), the Marais district including Place des Vosges. Paris walks, cousin to London Walks, has good tours there. And lunch or drink at a cafe.

All of the suggetions on the board are good. Even though you will only be there two days (or maybe especially so) I'd buy a museum card (buy at metro stations). You can skip the lines at most museums and Sainte Chapelle. Do not stand in the regular lines - it seems weirdly rude to do so but - go to the front of the line, show your museum card and you will either be waived in or directed BIT of the Louve, Sainte Chapelle...do go upstairs as that's where "it's at" (there is a security queque since it resides inside a police compound usually o/a 20 min.),the Orsay (great lunch)easilly with two days (not well mind you - more like a tasting menu!) The metro is easy to use (the maps have a start/stop point so you can figure out which way on any give line you want to go). Stike is pretty much over.

You should do the Historic Paris walk from Rick's book that includes Notre Dame, the deportation monument, Left Bank stuff, Sainte Chappelle (Do NOT miss this). You can also do a tiny bit of justice to the Lourve and M D'Oursay in one day. We just got back and packed almost everything in four days and that was even walking everywhere except Versailles. Read up on closing dates because if you plan around the open/close days and the weather, you can see a ton. Have fun! We sure did.

Does 2 days in Paris include travelling and checking into a hotel or is 2 days the actual free time you have?

If you have 2 full days, you can do a lot. You will need to get up early both days and you must visit the Notre Dame and climb the steps. You must Visit the Eifel Tower and go to the top. You must visit and climb the Arc De Triomphe and you must see the Mona Lisa at the Louvre.

After that, you should really just walk around and enjoy your surroundings. Stroll through Jardin de Tuilleries and down Champs Elysees. Just walk around as much as possible and take it in. Eat at cafes and enjot the food.

I would spend at least one day riding the Batobus and walking around wherever it stops.

http://www.batobus.com/english/boat-cruise-paris-seine.html

My favorite stop would be St. Germain des Pres, where I'd walk on the rue de Buci, have a gelato at Amorino, and sit by Saint Sulpice. The views are great from Cafe de la Mairie. I also love the cafes, Cafe de Flore and Les Deux Magots, even though they are a bit expensive and can be touristy.

Sandy

The Wedding at Cana (in the Louvre across from the Mona Lisa unfortunately), The Coronation of Napoleon (Sacre of the Emperor Napoleon I and the crowning of the Empress Joséphine in the cathedral of Notre-Dame of Paris", by Jacques-Louis David) (at the Louvre or copy at Les Invalides) are two of my favorite things to see in Paris. I also very much enjoy the Renoir at the Musee d'Orsay. I would choose small areas of these museums to visit.

I really enjoyed going up the Arc de Triomphe because of the wagon wheel view spreading out from the base, plus the fact that you can see the Eiffel Tower and Notre Dame. Very fun! Have a fantastic trip!

My thoughts:
Day 1: Notre Dame, St. Chapelle
and walk around the Ile de la Cite and Ile St. Louis.
Have lunch at a nice cafe
Stroll in the Marais
Go up to the 2nd level of the Eiffel tower at sunset.

Day 2: (this assumes you want to see some of the great art of Paris)
See the biggies at the Louvre
Go to Angelina's for hot chocolate.
Do the D'Orsay.
Weather permitting -- take a Seine boat cruise, or just stroll the banks.

And have at least a couple of nice lunches or dinners in a cafe or restaurant -- try to go to one recommended by Rick or other guidebooks.
this is my recommendation anyway!

My favorites were the Eiffel tower at night, Rodin Museum, D'Orsay Museum, and a boat trip.

2 full days in Paris is a nice amount of time to sample the city. The Eiffel Tower - best view from level 2; the Seine River - at dusk if possible; Notre Dame (the tower is spectacular as Joann stated); Sacre Ceour (Rick has a nice walking tour in the area); hit the highlights of the Louvre - the must sees Mona Lisa/Winged Victory etc; I prefer the D'Orsay; and I wholeheartedly agree with Ian about climbing the Arc De Triomphe. Remember you cannot see it all - but you will get a nice flavor of the City. Happy travels.