Miss Identify is an excellent utilty which can be used to detect executable files on windows, regardless of their file extension, it is very similar to "file" tool in unix but it is has a special task, Detect only executables only. The tool looks very promising.
"Miss Identify is a program to find Win32 applications. In its default mode it displays the filename of any executable that does not have an executable extension (i.e. exe, dll, com, sys, cpl, hxs, hxi, olb, rll, or tlb). The program can also be run to display all executables encountered, regardless of the extension. This is handy when looking for all of the executables on a drive."