Any major courier company would do. I send drives all the time. I just buy them and bill it back to the client. If they don't want the drive you can just have them send it back.
Personally I just buy what's on sale :)
Just find out what kind of system they are on, so you can format the drive accordingly.
Never send one anywhere until you are sure you have one and preferably more backups retained where you are. Typically packages like this are only insured for the value of a blank drive mechanism, not the multi-million-dollar value of the footage on it.