I have not heard of a utility that does such a thing. However, searching for ".esp", ".esm" and ".omod" files with Windows search should work just as well as any utility. It could not distinguish archive types that are not specific-to Oblivion from other files if they are packed in a regular archive or something like that. I do not know what you mean by mods not having to be in the data folder though. A utility used to search for certain file extensions would not be limited to your Data folder.