Lodging recommendations

Budget? Shared room?

For me its about location. Access to the Metro/RER & sites. I prefer to stay near the Saint-Michel Stop. Here you can catch the Metro-4 which cuts North to South of Paris as well as the RER-C which is East - West & Versailles. The RER-B is also at this stop which runs North to South, to and from CDG Airport. Notre Dame is just around the corner as well as St. Chapelle. I have stayed at the Hotel Europe Saint Severin,http://www.hoteleuropesaintseverin.com, others have mentioned the Hotel Le Regent,http://www.hotelleregent.com, both within a short distance from Saint-Michel stop. Plenty of shopping, restaurants and eateries in the area.
I guess it all depends on what you are looking for and what area you wish to be in or near.

You're not giving us much to go on, but I'll suggest as a "hidden gem" the Hotel des Grandes Ecoles in the Latin Quarter, where we spent 12 nights years ago. It's near a couple of Metro stations, the Mouffetard street market, and Place Contrescarpe. But there are a great many fine hotels in all price ranges and many neighborhoods. You'll get more recommendations from others on this board. Good guidebooks can also help a lot. Use Google Earth "street view" to scope out the surroundings of places that interest you. Or, alternatively, use it to find websites for hotels in neighborhoods that interest you. St-Michel, as suggested above, would be a good choice though maybe a little busy and noisy.

Rooms will be smaller than we're used to. If there isn't an elevator, remember that a "first floor" room is on what we'd call the second floor. Try for a room in the back to reduce nighttime street noise (unless your priority is viewing the street life from your window). Breakfast is usually extra, and usually overpriced compared to what will be available at cafes within a block.

We like the Hotel Emperuer in the 7th, http://www.hotelempereurparis.com/. Across the street from Les Invalides, the Eiffel Tower is within walking distance and Rue Cler is 3 or 4 blocks away. The metro is across the street and there are several restaurants and bakeries in the area. We also like the sister hotel which is on the same block, http://www.hotelparismuguet.com/. There is also a laundromat on this block, which turned out to be a fun experience!

Don't know how long you will be staying in Paris, but you might consider an apartment, for about the same price of a hotel. This is our favorite option. You can have coffee and croissants in your apt. every morning and you will have a washer and dryer, allowing you to pack less. We have had a great experience with this company. http://www.parisvacationapartments.com/

Have Fun!