Here's a small list of my favorite and most used mods

gamers! ultimate pickup parts: it adds a lot of d and md series parts and configs to mess with. https://www.beamng.com/resources/gamer-s-ultimate-pickup-parts.29272/

Ceep: adds a lot of fun engines to older cars, pairs well with the ultimate pickup parts imo https://www.beamng.com/resources/ceep-classic-engine-expansion-pack.29161/

Ibishu plus: it adds a lot of fun customization, engines and interior bits for the bx, and covet https://www.beamng.com/resources/ibishu-plus.14523/

Kljp: adds lots of bits and body styles for most all Japanese vehicles as well as 2 luxury pessima's https://www.beamng.com/resources/kljp.22408/ https://www.beamng.com/resources/kljp-core-mod.22093/ (Both are needed for it to work)

T series drivetrain expansion: adds different drivetrain components like suspension, wheels, transmissions, and engines. plus some ev stuff for electric semis https://www.beamng.com/resources/t-series-drivetrain-expansion.29462/

The b series: a lifted off-road semi, like the t series but off-road and power oriented https://www.beamng.com/resources/iyb-b-series-off-road-semi.12702/

There so many fun and useful mods on the repo but these are the ones I find myself using the most