Now SparkFun Electronics, a great electronic components distributor, has EasyUSB on its catalogue:

The EasyUSB gives your microcontroller access to 2MB that can be seen as a mass storage device in most operating systems. Now your microcontroller can easily read and write files in a file system that your computer can easily understand.

More than a simple mass storage system, it allows the implementation of a serial communication link between software and device without drivers’ headaches… that’s an easy and fast way to get USB connectivity on custom devices. Check the datasheet and the SDK.

The modules can be ordered on its website.