EU in Barcelona recommends these residences as they have an English speaking staff:
Residencia Onix
Barcelona Residencias
Residencia Melon District
San Marius
Apart from that, there are websites that you can look for housing independently, these websites a whole range of budget choices that make it affordable for students to live in:
idealista.com
homestaybcn.com
bcn.es/ciaj
altiro2000.com
barcelona-allotjament.com