If you want only a disassambler / debugger you could take a look at OllyDBG or Immunity Debugger ( a clone of olly but has better Python Scripting support and several improvements ). For a decompiler you should look for each programming language for a own one. But IDA is one of the best tools you can get for malware analysis and you can extend it easily for new formats / file types, with plugins, py support etc ( I just love it).
~Zer0Flag