These are the core add-ons for the stock game that add more realism, but don't mess with the tech tree or add a ton of parts. The core game plus it's expansions have a boatload of parts now, and I find most everything I need in it.
Certain addons are not currently available on Spacedock, but can be downloaded via the CKAN app:
MechJeb 2
Waypoint Manager
Strategia
PlanetShine
Kopernicus can be downloaded from it's GitHub page:
### SphericalTanks
- Five (5) 1.25m spherical tanks. Available in veteran orange.
### CargoBays
- Three (3) 2.5m rocket cargo bays in 1m, 2m, and 4m lengths. Flat fold doors.
### AeroRadial
- Two (2) streamlined, radially attached power products. One RTG, the other a Liquid Fuel and Intake Air powered fuel cell.
### Fuselage
- Seven (7) flat fuselage pieces.