Do you want themed racing games in different time periods?
If you’re using realworld(or alikes) cars, there isn’t really much more to go for, you’ve got circuit, street, rally, drift and touring cars - which really the only thing you can start to really differ is locale or time period.
F1 is F1 and F1 fans will slaughter anyone who tries to mess with F1. But also there are yearly games, since the rules change every year and the new game is the new rules.
Do you want more arcade style?
What are the indie games that have piqued your interest?