My top ten:
Gran Turismo 4
Before GT got too big and where every aspect was polished. GT6 still has my favourite physics in the series, but PD still hasn't cleaned up a lot of aspects that need to be brought up to snuff.
Daytona USA (arcade ver.)
The feel of this game is glorious. This list could probably be Sega racers alone with how many stellar versions of Initial D, Daytona and Sega Rally there are, but Daytona USA takes it for how far ahead it was on release. Daytona USA made PC racing games look bad till the end of the decade.
Project Gotham Racing 4
Essentially PGR3 but more, this was PGR at its sharpest. Motorcycles, terrifying weather, still ridiculous graphics, smooth feel. PGR2 might be the more influential game given its release at the dawn of XBL, but I still prefer PGR4 for bringing more all at high levels of polish.
Burnout Revenge
The logical step after Burnout 3. Everyone and their mother likes Burnout 3, but Revenge gave us what such an aggressive game should have been in the first place without losing any of the danger from the previous games.
F-Zero GX
GX at its hardest commanded as much finesse and focus as sim racer combined with the aggression of Road Rash. Still a looker after all these years, I wish AV came back to make another one of these.
Wipeout HD/Fury
Zone mode is pretty much REZ. Wipeout and F-Zero is always pitted against each other, despite the drastically different feel. The floatier, slower controls of Wipeout combined with the audiovisual experience of Zone mode results in a zen I rarely reach with racers.
Pole Position (arcade ver.)
The granddaddy for how we experience racing games now. Yes, it does borrow a lot from Sega's Turbo from a year earlier - the behind the car view, different tracks/stages, sit-down cabinets, etc. Pole Position improves on it with its motorsport focused design and making it about the racing, not "lives" or anything like that.
Forza Motorsport 4
When Forza learned to have a soul. Forza has always been a great series but has often been derided as clinical in its approach to car culture and history. It took the ex-Top Gear hosts to help show T10 how to show it, but AutoVista is the addition Forza needed to stop being a racing game and start being a car game. And for a game that offers as much as Forza, I think it needed this.
Super Mario Kart
Super Mario Kart showed the joy of racing to a larger audience. It might not be fair in that the fastest racer doesn't always win, but part of the appeal in Super Mario Kart is that everyone has a chance. Giving people that chance makes every race entertaining no matter the odds.
Need for Speed Most Wanted (2005, 360 ver.)
The best of the Black Box racers. The style, the FMV cheese, the difficulty, the cops finally being back. The absolutely iconic M3. The physics being brought closer to weighty, drifty goodness after NFSU and U2. This is what you need to play if you're new to NFS.