One thing you might come across as you unzip more mods is sometimes the actual mod folder is zipped up inside other folders - making it confussing if you automatically unzip everything straight to your SH3/MODS folder. It doesnt happen often, but sometimes you'll unzip something and it will be contained within its own MODS folder, or the mod folder will be doubled up - ie "your_new_mod/your_new_mod/data".
Out of habit I find it best to unzip everything to the desktop 1st so I can see straight away how the folders are set up and then just cut and paste into the SH3/MODS folder.
Sorry it's not a very clear explaination, but if you come across a mod that isn't showing up in JSGME for some wierd reason, most times it's due to this.
Happy hunting!