Paris is one of the great fashion centres of the Western world, up there with New York, London, and Milan, making it a shopper's delight. While the Paris fashion scene is constantly evolving, the major shopping centres tend to be the same. High end couture can be found in the 8th arrondisement. In summer, there is nothing better than browsing the boutiques along Canal St-Martin, or strolling along the impressive arcades of the historic Palais-Royal, with beautifully wrapped purchases swinging on each arm.
A good note about Le Marais is that as it is a mostly Jewish neighborhood, most of the shops in Le Marais are open on Sundays. The stores in this area are intimate, boutique, "Parisian" style clothing stores. You will no doubt find something along each street, and it is always well worth the look.
Other great areas to shop around in are around the area Sèvres Babylone Métro Line 10 and Line 12. It is in this area you will find the Le Bon Marché 7th, particularly rue de Cherche Midi 6th. The area boasts some of the major fashion houses Chanel, Jean Paul Gaultier, Versace, etc and also has smaller private boutiques with handmade clothing.
In the Quartier Saint-Germain-des-Prés, you can find a handful of vintage clothing shops, carrying anything from couture early 20th century dresses, to 70s Chanel sunglasses. Walking along Boulevard Saint-Germain, you will find major brands. However, if in search of eclectic finds, opt to walk the northern side of the Boulevard, especially along rue Saint André des Arts, where you can always find a nice café to stop in. The area south of Saint-Germain is just as nice, and comes with a price tag to match.
In the artsy quarters of 1 and 4, there are many bargains to be had, once again, if you are prepared to look. Souvenirs are easily found and can be fairly inexpensive as long as you don't buy from the tourist sites. For cheap books of French connection, try the University/Latin quarter as they sell books in all languages starting from half a euro each.
musical instruments
Rue de Rome, situated near Gare St. Lazare, is crowded with luthiers, brass and woodwind makers, piano sellers, and sheet music stores. Subway station Europe. The area south of the metro station Pigalle is also packed with music shops more oriented towards guitars and drums.
artwork
For art lovers, be sure to check out Quartier Saint-Germain-des-Prés, which is renowned for its galleries, and it is impossible to turn a street without finding a gallery to cast your glance in. On Fridays, most open until late. Most even have the benefit of bottles of wine so you can wander in with your glass of wine and feel very artistique. Great roads to walk along are rue de Seine, rue Jacob, rue des Beaux Arts, Rue Bonaparte, and Rue Mazarine.Also, be sure to visit the historical district of Montparnasse' and quartier Vavin where painters like Modigliani, Gauguin and Zadkine used to work.
flea markets
Paris has 3 main flea-markets, located on the outskirts of the central city. The most famous of these is the Marché aux Puces de St-Ouen Porte de Clignancourt Clignancourt Flea Market , Métro: Porte de Clignancourt, in the 18th, a haven for lovers of antiques, second-hand goods and retro fashion. The best days to go are Saturday and Sunday. Note that there are particular times of the week when only antique collectors are allowed into the stalls, and there are also times of the day when the stall owners take their Parisian Siesta, and enjoy a leisurely cappuccino for an hour or so. The best times to visit the Flea Markets are in the spring and summertime, when the area is more vibrant. In and around the metro station, you may find the area a little wild, still safe.