I am searching a tool which allows to encrypt a whole harddisc and not only
a volume file as the most of the offered tools.

Yes, I know TrueCrypt. But this tool has problems with large external USB drives.
I got permanent errors from the TrueCrypt driver in big operations like
copying 20000 files onto a TC encrypted harddisc (Doing the same with
the same USB hatrddisc unencrypted show no error).

Yes, I know also PGPdisk. But this tool can only exist with a running PGP installation.
I need a tool which can be launched easily on demand (when I plugged in the external USB drive)

BestCrypt, DriveCrypt offer only encryption of volume files.

Which tools exist otherwise?