Here are some links I've collected for following real world racing:
Twitter accounts tend to link to their official websites.
Series and governing bodies:
https://twitter.com/IMSA
https://twitter.com/FIA
https://twitter.com/F1
https://twitter.com/GP2_Official
https://twitter.com/FIAformulaE
https://twitter.com/indycar
https://twitter.com/indylights
https://twitter.com/UnitedSportsCar
https://twitter.com/FIAWEC
https://twitter.com/EuropeanLMS
https://twitter.com/BlancpainGT
https://twitter.com/24hseries
https://twitter.com/AsianLMS
https://twitter.com/WCRacing
https://twitter.com/gt4cup
https://twitter.com/BritishGT
https://twitter.com/BritcarNews
https://twitter.com/SF_SGT
https://twitter.com/gtmasters
https://twitter.com/GT_Tour
https://twitter.com/GT_Open
https://twitter.com/SupercChallenge
https://twitter.com/dtm
https://twitter.com/FIA_WTCC
https://twitter.com/DunlopBTCC
https://twitter.com/FIA_ETCC
https://twitter.com/v8supercars
https://twitter.com/NASCAR
https://twitter.com/OfficialWRC
https://twitter.com/FIAERC
https://twitter.com/fiaworldrx
https://twitter.com/_TropheeAndros_
https://twitter.com/dakar
https://twitter.com/FormulaDrift