I absolutely love WipEout. It was one of the most impressive looking games on the Playstation. it's design made it significant in my life. Wipeout 3 SE is my favorite of the series, followed by HD Fury, which eliminator is practically therapeutic. And special props to Quantum Redshift on the Xbox, which filled a gap in my life where not having a PS2 left.
Now Mario Kart is good and all, but I'd say Crash Team Racing tops it, especially if your drift game is strong.
I also like the Trackmania series, especially Canyon. It has probably the best control i've ever felt in a racing game, and that matters a lot. Plus, occasionally I spend hours building tracks.
Basically, anything that doesn't require too much effort to just go around a circuit is good enough for me. That's why I believe in Drift Stage. It feels tight, its not hard to respond like most SOREAL racing games are, but it's two tiered. to drift or not to drift. That's just right!
Also a special shout out to Monster Truck Madness 2, in which much fun was had going off track and exploring with occasional hilarious results. And made up the majority of good memories in my final year of Primary school (especially since I pretty much discovered TCP/IP network play with it and it became massive)
And to Need for Speed II, especially the Lotus Esprit V8 which was left behind in Argentina last year.