Any underrated addons that make Gmod more enjoyable?

I'd check out gmodstore.com . They have many very cool addons that you will not find on the workshop.
Otherwise, here is a few vehicle things that I like:

WAC Aircraft pack
TDM Cars with VCMOD (from gmodstore)
GBombs is fun

But Multiplayer has a lot more to offer in my opinion, not addonwise but because it is way more fun to play with others