If you think of the best secure flashdrive to use, then that would be the IronKey Flash Drive.
All data stored on an IronKey drive is encrypted with a high-speed military-grade hardware encryption. Unlike software-based encryption, hardware-based protection is “always-on” and cannot be disabled.

The files on the IronKey USB stick can only be accessed once a correct password is authenticated. In addition to this, since the encryption and password verification are being performed on the hardware, it cannot be disabled by worms, viruses, or other malware.

You can read IronKey reviews here (IronKey Personal, Business, or Government), but the bottom-line are:

•Fast 30MBPS Read and 20MBPS Write (Compare this with the USB SuperSpeed 3.0)
•Drive contents are encrypted with AES CBC-Mode Encryption
•Onboard IronKey Password-manager keeping all your internet passwords safe
•Include secure version of Firefox that encrypts all your web-surfing traffic
•Encased in a potted metal case, not plastic (making it one of the strongest USB)
•Exceeds MIL-STD-810F military waterproofing standards
•The encryption chip self-destructs if an invasive attack is detected
•Once Ironkey is lost, you can restore from a secure backup to a new Ironkey in minutes
•Dual channel SLC NAND Flash for high-quality and read/write speeds
•Works great in Windows XP, Windows Vista, Windows 7 and Linux and Mac OS X (requires Windows intialization before working on Linux and Mac)

IronKey drive is not available outside the 50 United States. If you think the product is already available on other countries, just leave a comment below and also indicate the source so I can update this post.

You can also watch the video below for more info about the most secure flashDrive- the IronKey: