I have a work-in-progress list here, strictly games I would consider "must play" in the genre. Notably missing the Ridge Racer and Tokyo Xtreme Racer games because I haven't played enough of them to have an opinion.
Mostly arcade and simcade racers though. If you're interested in sims:
For modding, Assetto Corsa is basically the modern rFactor.
For offline racing, Automobilista and Raceroom have pretty solid AI. Note: Raceroom's pricing model is dumb, kind of like iRacing just without the subscription.
For career mode, Project CARS 2 (not 3) is basically the only sim that even tries.
For online racing, ACC and iRacing are unmatched.
For rally, you're already playing DR2. Richard Burns Rally is also shockingly good for its age.
I really liked the Tokyo Xtreme racer games. They are still probably the best car RPG games. I would love to see what someone could do now in the same vein. Even tokyo xtreme never got quite as crunchy or difficult as I would have liked.
I want to go so far as to be like a tactical survival style game, where you are out there earning a living wage from daily(nightly) car racing, and putting most of it back into your car. Just the repairs and maintenance alone being a bar you have to meet and beat every day on average to stay afloat, and then you can think about upgrades after.
It basically takes an environment like that for it to matter in a racing game that there are upgrades between the worst and the best. If trying to save up for even one good part wouldn't be possible without at least some middle parts first.
Meanwhile, could have some "roguelite" elements too in driver experience/skill. The car is only half of what's winning the races afterall. And even if you really blow it at some point and your car is fucked and you need to salvage and pull together what you got and go back to a cheaper car to maintain/repair, you'll still have all the experience/skill your character personally gained helping it go a little smoother this time.
There's also Night-Runners which is very much influenced by the TXR/Shutoko Battle games. It's an in-development crowd funded game, so take from that what you will, but there's a demo up on Steam as Night-Runners Prologue.
I contracted the iRacing sickness this year. The online is indeed unmatched but I'd argue the single player racing is also best in class.
The iRacing AI is actually fun to race against and nothing else comes close to the level of customization per-racer. You can build whole custom rosters with individual behaviors. If you're so inclined you can even share all this stuff through communities like Trading Paints and Race Department.
iRacing is a hole with no bottom. Both time-wise and monetarily. Even to do AI-only you're still paying the subscription and one-time content prices. It really is the best though.