There are dozens of ways to get to and from Paris' airports, from rapidfire shuttle trains to the standard assortment of pokey public buses, private shuttles and taxis. There's even a bus that runs solely between the two airports. Say what you will about driving around Paris, but the city's public transportation is world class.
The most charming of Paris' public transport options, the underground Métropolitain (and its sister system, the RER), is a simply massive network. No matter where you are, chances are there's a metro station within a few blocks. Likewise, the public bus system covers everywhere, but its hours are laughable and don't even try to hop aboard on Sunday or a holiday. The Noctambus network takes over in the heavily trafficked areas once both the underground and the day buses go to sleep.
In case you hadn't guessed it, driving around Paris is a job best reserved for the terminally aggressive - if you don't have lots of time to kill, you're better off taking public transport. Likewise with bicycles: Parisians don't much like to share the road, and bikes aren't allowed on the metro. There are river shuttles along the Seine, but these cater more to gawking tourists than to commuters.