MC Command Center by Deaderpool: Like this one is an absolute must for any Sim modder out there. Everyone who wants to mod their Sims 4 should have this installed, no questions asked. It's extremely powerful and it controls almost every facet of the game. Want to copy and paste your appearance and outfits onto another Sim? Want to play an 8+ member household? Want to play with testingcheatstrue right off the bat? Want to revive a Sim? Want to summon a Sim to your lot? Want to disable relationship decay? Want to slow down time? Want to add/remove moodlets from your Sims? Want to add traits? Want to disable certain autonomous actions for your Sims? Want multiple best friends? MC Command Center can do all of this, plus more.
Meaningful Stories by roburky: I always play with this on because this is just a much better emotion system in every way. It turns uncomfortable moodlets into boosters for negative emotions and its emotional inertia system stops Sims acting like light switches or liking a decoration even while they are mourning. Your Sims will actually get pretty furious and depressed for once.
Color Sliders by thepancake1 and MizoreYukii: This is the closest you will get to a color wheel for the Sims 4 in CAS and I strongly recommend it.
EcoDisc 52X Mini Weather Controller by lot51: If the current weather control machine is a bit too limited for your tastes and you're looking for something to control the weather (hard to get by and cumbersome to use cheats), then this is the mod for you. This comes with Thundersnow, Sun Showers, Dry Lightning, and more!
Torture & Chaos by Dramatic-Gamer: I like using this to lightning strike, stink up, and deprive needs of the paparazzi in my lot and this one comes in handy for me.
Pose Player by Andrew: Extremely handy to use if you're looking for a specific animation and sound and you don't feel like manually activating them to get them in that pose throughout the game. Only downside is that animation lists aren't updated so you're sorta forced to extract their names with Sims 4 Studio by parsing through like the GP, EP, etc files in your installation.