The Unofficial patches by Arthmoor are a must-have for me. Other than that, it's really dependent on playstyle. If you like maximum difficulty, Deadly Combat, Deadly Dragons, Dragon Combat Overhaul, are all good mods; I also recommend Run for your Lives, and When Vampires Attack if you get those, or npcs will drop like flies. If stealth is your thing, try Borgut1337's Sneak Tools, as well as Follower Trap Safety, Traps Make Noise, and Better Stealth AI for Followers. Trade and Barter is good if you spend a lot of time playing with money, or end up with millions of gold toward the end of the game. The most recent two mod sanctuary videos by Gopher cover some fun Werewolf mods. If you make a lot of new characters, rather than focusing on one, you might like Alternate Start - Live Another Life by Arthmoor. He also does an Open Cities mod, but that one is taxing on the system by its very nature (so a lot of people have unstable gameplay). I could go on, but what I recommend is going into the individual categories on nexus, and sort by most endorsed of all time. Often the top mods are good, and they'll often have links to other mods that they feel compliment theirs or that they support for other reasons.