There are several companies that organize Seine cruises and we chose to go with Les Vedettes du Pont Neuf simply because it was easy to find where to embark: the boats leave from the Square du Vert-Galant, at the western tip of Ile de la Cite (you'll see a big sign as you're walking on Pont-Neuf, near the Henri IV statue). A lot of people had told us the best time to go was at sundown so we embarked at 9:00 pm. It was indeed a great new way to look at the city we had come to know fairly well at this point of our trip. The upperdeck was full and there was a great atmosphere on board - kids laughing, a 2-month-old baby getting its picture taken in front of the Eiffel Tower, an elderly couple holding hands... it's Paris at its most romantic!
The cruise lasted a little over an hour and our guide Alexandra gave us a lot of information about the buildings on both sides of the Seine, and what I thought was the most interesting is that she also gave us a lot of information on all the different bridges we crossed, which is not something you find in most tour guides. So all in all, it was a great experience!
The cruise costs 11 Euros, but if you visit the Website you'll find printable discount coupons. From March to October there are departures every 30-45 minutes, from 10:30 am to 10:30 pm, every day of the week (see the Website for more information). The boats are fairly big (capacity of 300 people) so it's not necessary to make a reservation and you probably won't have to wait long before you get on board. | 
