Mod.esp (your mod's ESP file)ReadMe - Mod.txt (your ReadMe document)fomod/info.xml (title, author, category, version information)
At least, that's how I structured my release ZIPs (uploaded as .zip instead of .fomod due to Fallout3Nexus rules).
Now I have a few questions:
1) If I want to include additional ReadMe type files in the ZIP, but don't want them to get installed to the Fallout 3 program folder, do I just put them in a sub-folder inside the ZIP and FOMM will ignore them?
2) Are there any issues with naming the file .ZIP instead of .FOMOD since FO3Nexus won't let me upload as ".fomod"?
3) If I stay away from scripting, do I need to care at all about the FOMM version? I think the answer here is no.
4) Any problems with assembling the ZIP by hand, including editing the info.xml file with a text editor?