Don't take a car to Paris, you won't use it.
Absoultely the Eiffel Tower. There could be no one favorite thing about Paris, it's a wonderful place. Create your own memories. I rented a car at the airport, and promptly drove to the city, where I immediately parked it in a garage until I was ready to leave for Dijon. I didn't use the car a single time. It won't take long for you to figure out the Metro and normally you come out right where you wanted to be. And hey, you are instantly mingling with the locals.
And should you speak little French as did myself, just learn the very basics. Yes, No and Thank you. I used them all quite frequently. It sure doesn't hurt to add 'Can you tell me where is----------?' Hmm, my fondest memory. I can't think of one in particular. Waking up to hotel breakfast of the best coffee and pastries you can imagine, or seeing the Eiffel Tower, sitting at cafes people watching, walking along the streets and along the Seine.
If you've never been on the...
If you've never been on the bateaux mouches, you will enjoy the couple of hours you spend cruising on the river and getting your bearings. You will get a good idea of how the city is laid out, as well as a general overview of the city's history.
I was a kid in Quartier Latin
When I checked over the net where places whose I have most vivid memories were, they ended up being in Quartier Latin.
As a matter of fact, I experienced many things in the area. One of nicest and exciting discoveries in Paris was La Menagerie des Jardins des Plantes. I remembered my parents and my uncle took me there in an afternoon. It was a real running-off !
It was not my first time in a zoo but it was the first time I could see the Big 5. Also, bears were very impressive. Anyway, my preference goes to reptiles (saurians, not snakes) and bears. I saw some yacks, watussis.. weird. Never liked baboons and monkeys. The ones I hate least are, of course, lemurs. Well, I like lemurs but really hate the big beasts like orang-outangs, chimpanz?s...
Also saw a big fat yellow anaconda from.. Madagascar. Aaah ! Made me think of some lemon yellow plastic design, about everything but an animal. It was so bright yellow like lemon. Then, also remembered throwing coins to the crocodiles there.
I also appreciated strolling around, just spotting here and there flamingoes, ostriches and the many goat-types. My first visit was in mid-80s. In 2000, we returned there again and I saw kangaroos. First "in flesh" encountering with TV stars. :)
After the menagerie, we went to one of the cafes around. I remember I had blueberry cassata there while my Mum and I were waiting for my father and uncle. The guys went checking the car they parked somewhere. Parking in Paris is not easy. Well, it's hell ! At first, I hesitated about the name. Either it was Zoo de Vincennes either Menagerie des Jardin des Plantes. Anyways, there have to be animals :). Then checked over the web some pics which would help me to recognize the park I really visited.
I saw some pictures I recognized immediately. Then, saw the location: in Quartier Latin again. Not that surprising. My parents, esp. Mum, loved the area.
Built to replace the Royal menagerie of Versailles in 1794, no wonder it still has an old-fashioned ambience and setting. Maybe this intimate aspect was what made me love it.
The best website I found on La menagerie was the following (in French). Well, at least, it helped me to remember the name accurately. :) Lots of pics there.
Don't be ticked about the toilets
When I was in Paris, I usually had to pay a Euro if I wanted to use a public bathroom. This isn't the case with EVERY Parisian toilet, but usually in large shopping centres and some museums you need to deposit change in order to open the stall door to the toilet. Otherwise there'd be a lady sitting outside the washroom and I'd have to pay her cash so she would give me a key to open the stall. I'm not sure if it's like this in other parts of the world, but where I come from it certainly isn't the case. Make sure you have some change on you at all times incase you need to use the washroom ( you don't have to pay if you're just going in there to check your hair or change a baby.) Those things are free of charge.
Masters Series Paris
Each year at the end of October, the Masters Series tournament in Paris gives you a good oportunity to see good tennis players cheaper and easier than going to Roland Garros for the French Open. I went in 2005 and saw Roddick (pictured), Lubicic, Berdych, the Bryan Brothers, and more. It's good indoor tennis and tickets aren't hard to come by. They play at the Palais Omnisports de Paris-Bercy.