I've linked to this site a few times recently after reading about people despairing about expensive 0845 numbers - particularly in public services, but thought it deserved a thread of it's own.
If you are given an 0845 or other 08 number to call, check this site first to see if there is an alternate freephone or landline number:
SAY NO TO 0870
Even if the alternate number doesn't get you to the correct department, you can usually then get an internal transfer.
Its saved me a fortune!