Bateaux Mouches is one of the companies selling river cruises on the Seine.  There's also Vedettes de Pont Neuf that Norene and I used when we were there in 1996.  They just cruise up and down and the guide points out all the sights, odd architectural details about some of the buildings, and they give you advice about what to see after the cruise.  This is a picture of one of their boats taken from the balcony at the Musee d'Orsay.  As you can see, they hold several people...  at 60-80 FF per head this is not a boat, it's a gold mine.
When we visited Cluny, we picked up a 5-day Museum Pass.  This wonderful device allowed us to go to the head of a 2-block-long line of people waiting to pay their way into the M'O.  The passes were about 250FF ($30?) each, but I would have paid that just to avoid the line that day.  It's worth it just for the convenience.
Across the river you can see to the right a Ferris Wheel at the Jardin des Tuilleries, and in the center, far off on the Butte Montmartre, the domes of Sacre Coeur.