Hopper Disassembler is a binary disassembler, decompiler, and debugger for 32- and 64-bit executables. It will let you disassemble any binary you want, and provide you all the information about its content, like imported symbols, or the control flow graph! Hopper can retrieve procedural information about the disassembled code like the stack variables, and lets you name all the objects you want.
Hopper is able to transform the assembly language into a pseudo-code that is easier to understand! You can use its internal Python scripting engine to analyze binaries the way you want (this feature works only with Lion)! Starting from version 2.0, Hopper can even use GDB to debug programs!
And, last but not least, unlike all other tools of its kind, Hopper is perfectly integrated into the OS X environment.