The German Privacy Foundation CryptoStick is a combo OpenPGP smartcard and reader that's about the same size as a thumb drive.

It allows you to store your OpenPGP keys on the smartcard.  Once on the card, they can't be extracted.  The private keys never exist on your main computer's hard-drive or in its memory.  This means that they can't be extracted by a malicious user or a virus.  Compared this to the normal software solution, where your private keys can be retrieved and subject to offline attack, or compromise in combination a keylogger.

In addition, the card itself has a self-destruct capability, which prevents an attacker from brute forcing the card itself if it's stolen or lost.  Three incorrect password attempts locks the card.  It can be unlocked with an admin password.  Three incorrect attempts with the admin password will cause the card to self-destruct, wiping the keys from the chip itself.  (The card can be reset to factory defaults after this happens.  It doesn't catch on fire Mission: Impossible style.)

This particular card is slightly used, and missing the end cap, but it has been restored to factory defaults.  But I can ship it to anywhere in the US for 10 BTC including shipping.  You can buy a brand new one easily enough, but it's about 50 Euros, plus shipping charges from Germany.

More details on the card here:

http://www.privacyfoundation.de/crypto_stick/crypto_stick_english/