According to TransferMarkt.co.uk the following players are entering final season of their current contracts:

4. MORRISON, Sean (C)
5. FLINT, Aden
6. VAULKS, Will
8. RALLS, Joe
11. MURPHY, Josh
14. VASSELL, Isaac
17. TOMLIN, Lee
21. PACK, Marlon
25. SMITHIES, Alex

Bonus:
26. GILES, Ryan (end of loan deal)
30. BROWN, Ciaron (no information on when contract expires)

Contract renewals are going to be as big for us this year as new signings and will tell us a lot about what sort of side we'll be going forward.