Barcelona is a shoppers' paradise, there are shops everywhere, and there are several shopping centres scattered across the city where you will find mainstream international brands and also some local and independent shops too.
Opening times for shopping centers in Barcelona are from Monday to Saturday from 10am to 21:30pm for shops, the rest of facilities are opened until later such as the restaurants and the cinema. The only shopping center in Barcelona that opens on Sundays too is the Maremagnum, in case you would like to do some last minute shopping before leaving.
La Illa: One of the nicest and tidiest shopping centers in town, it is located in the posh area so no wonder why it is one of the most exclusive ones, get ready your credit card since the brands located are in the majority high end. You can also find affordable ones such as Primark for example, but they are the minority. Recently it opened an Escribà bakery and a Brunch and Cake shop, perfect for an afternoon snack or a breakfast in style. You can access by metro: L3 Maria Cristina.
Les Glòries: It is the shopping center located in Les Glòries square, it is a big shopping center with different levels and has a cinema in it and a carrefour supermarket too. It is the nearest shopping center to Sagrada Familia area. You can access by metro L1 Glòries.
El Maremàgnum: A shopping centre by the sea, has three storeys and sells mainly clothes and has also restoration area. This is the only shopping center that opens on Sundays. You can access by metro L4 Barceloneta
Diagonal Mar: This is Catalunya's biggest shopping center and is located in the Forum area, where there are concerts in different times of the year. You can access by metro: L4 Maresme/Forum
La Maquinista: it is one of my favorites, since it is outdoors although it is covered in many parts, you feel the fresh air and they have a wide variety of shops, they have full floor for restoration options and a cinema. It can be accessed by metro Torras i Bages.
Les Arenes: It used to be a bullfighting arena and now is a shopping centre that also has the Museum of Rock inside. It is in Plaça Espanya area and the place is famous because of their roof level that has an outdoor promenade of 360º, you can see the city from above. It can be accessed by metro L3/L1 Plaça Espanyal
Gran Via II: Gran Via 2 is located in Hospitalet, at about 2 km from Montjuic, the place is interesting due to its classical design that recalls Roman times. It has more than 200 stores and in the top floor a restoration area and a cinema. It can be accessed by FGC Ildefons Cerdà.
Heron City: it is an outlet shopping center in Barcelona, it is not very big so do not expect a wide offer, it is more a local mall of the area and it is located in a neighbourhood that has no touristic value. You can access by public transport with metro L1 Fabra i Puig or L5 Virrei Amat.
El Triangle CC: This is a small mall in the heart of Barcelona, right in the same plaça Catalunya. Mainly clothes and shoe shops along with a couple of cafeterias and places to eat. It can be accessed by metro L3/L1 Plaça Catalunya.
Boulevard Rosa: it is a hidden shopping centre inside a block in Passeig de Gràcia that has different entrances since it occupies a full block of houses. The location is very convenient and it is full of local brands and also international ones. It can be accessed by metro L2 Passeig de Gràcia.
Disclaimer: Picture from Maremagnum shopping centre by Antonio Gil, no changes were made to the original.