The stations are similar to London - they ring around the city centre and serve the area beyond. If you are coming from the UK, then Gare du Nord is where you come in. Austerlitz serves the Loire Valley and South west, but it is close to the centre (Notre Dame), as is Gare du Lyon.
Eiffel Tower if you have time to spend in the queue. La Louvre is good, and if you only have a short time, the route to the Mona Lisa is marked.
Personally, I like to hang out in the St Michel area. The other great area is Montmartre/Sacre Coeur.
The area around Gare St Lazare is a good example of shopping (famous department stores) and restuarants.
I always recommend people go to the Tour de Montparnasse (which might tie in with your travel plans). Fabulous views of Paris, with the added advantage of being able to see the Eiffel Tower (and have it in your photos).
Here is the RAPT interactive map in case you haven't all ready found it. Many of the RER stations are linked to the Metro. If you want to see a few things around paris i would recommend getting a day ticket or a carnet of tickets and jump on and off Metro to save the legs and fit more in.