After years managing rfactor 1 leagues this is my top. Based on various things and on members reports.
(not in any particular order and obvious lacking some)
- Historic GT & Touring cars by Historix modding team
- DRM Revival by DRM Modding Team
- V8 Supercars by ORSM
- Endurance Series by Enduracers
This are the best of the best. Then you have a second level ones where you can find dozens of great mods like:
- All open wheeler mods by F1SR
- Blancpain Series by Gpfan & Alex Koda
- Touring Car Legends
- Rallyworld mod (so much work done in it, so much models).
- Etc
Theres much more good mods that´s hard to place them all like Formula Armaroli, Formula Renault 2.0......
EDIT- Just to understand the dificulty....check here and remember that a large percentage of the current avaliable mods are NOT there:
http://www.rfactorcentral.com/sitemap.cfm