Not a lens suggestions as such (I'd take all of them, personally), but if you get time, visit the Musee D'Orsay (near the Louvre - on which do not waste time). The photographic exhibitions at the D'Orsay are a unique tour of the great French photographers, and it's a stunning building. (formerly a very large railway station, tastefully and expensively converted to its new role).
Also stuffed with Rodin, and the largest collection of Impressionist painting I've ever seen (how many Monets do you want?). Also good around that area for "Paris Garden" photography. (can't remeber the name of the gardens across the bridge, but they are famous)
The Opera (Place de L'Opera) is also worth looking at - go in the day and you can usually get inside at not cost. Incredible interior.
Keep the kit concealed or discreet when you are walking around. Some black sticky tape over logos helps, as does a cheap/nasty looking neck strap. Paris, like London, isn't as safe as it used to be.
Oh - for night photography from tripod - visit the French Grand Prix (otherwise known as the Champs Elysee). Six lanes of Gallic petrol-head madness, with the L'Arc de Triomphe as a background - terrific for long exposure. Just cross with care!
Have a great time
Regards
Ewen Cameron
Kent, UK