diStorm is a binary stream disassembler. It's capable of disassembling
80x86 instructions in 16, 32, and 64 bits (AMD64, X86-64). In
addition, it disassembles FPU, MMX, SSE, SSE2, SSE3, SSE4, 3DNow!
(with extensions), new x86-64 instruction sets, VMX, and AMD's SVM! 
diStorm was written to decode every instruction quickly and accurately,
with robust handling of valid and unused prefixes. It supports
multi-threading, which means you can disassemble several streams 
simultaneously.

WWW: http://www.ragestorm.net/distorm/