Dangerous Prototypes Buspirate
File:Buspirate v3 front.jpg
The Buspirate v3, front
The Buspirate v3 supports a logic analyzer mode and can thus be used for sample captures, however only at low speeds. To quote from the announcement: The Bus Pirate can’t store a lot of samples, it can’t feed live samples very fast, and speeds are in the kHz range.
See Buspirate/Info for more details (such as lsusb -vvv output) about the device.