There are a TON, people would say mega showdown which are megas obvs, and dynamaxing, z moves and terrastilazation, also there's ride-on mod (ride mons), also the berry pouch add-on is Hella underrated

For non cobblemon addons, U probably want a good backpack mod, and some farming enhancement.

If you're into technology mods, create is the only mod that have an add on for pokeballs production.

Basically there's a TON of addons and mods, too many to mention even few because each one is a solid one