Hi Eloisa! It depends on your starting level, but generally you can get:

English grammar in use/Advanced grammar in use - To improve your grammar skills;

Objective First - It allows to get more confidence with the arguments of this exam;

Firts Trainer - There are a lot of practice tests (with answers) where you can training on.

If you want to improve your vocabulary and listening skills, you could try:

Speak Up - A monthly magazine where you can find a lot of articles about various topics. There is also a CD with audio tracks about the articles.

Websites:

Go to Flo-Joe (google it). It's got lots of exam help.

The Cambridge English website has free exam material: http://www.cambridgeenglish.org/exams-and-tests/first/