Cool BBC Learning English Channel focusing on English at work.

https://www.youtube.com/watch?v=KN2jyw6D1ak&list=PLcetZ6gSk969oGvAI0e4_PgVnlGbm64bp&index=2

Free sample tests!
http://exams.richmondelt.com/index.php?practice_tests_pet_en
http://olpt.s3.amazonaws.com/online-practice-pet/index.html
http://eslcommunity.org/cambridge/pet-tests/pet-for-schools-practice-test/
https://sites.google.com/site/programabeda/home/alumnos/pet/pet-materials
https://clilcolonna.wikispaces.com/PET+Listening+Practice

Here's some grammar activities that may be quite useful for b1 and b2 students. The first three links are rephrasing exercises.

http://www.box.com/shared/lx5hicgs0i
http://www.examenglish.com/FCE/Use_of_English.htm
http://www.ompersonal.com.ar/firstcertificate/contenidotematico.htm
http://www.examenglish.com/TOEFL/toefl_structure_http://www.ompersonal.com.ar/firstcertificate/contenidotematico.htm1.htm
http://www.examenglish.com/leveltest/index.php
http://www.examenglish.com/ECPE/ecpe_grammar.htm
http://www.examenglish.com/grammar/B1_reported_speech.htm
http://www.examenglish.com/ECCE/ECCE_grammar.htm