Immortal Grand Prix, on TV Asahi (Japan) / Cartoon Network (USA)
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Caution: potential spoilers.

Immortal Grand Prix (or IGPX for short) was originally a microseries in 2003, consisting of five 5-minute episodes. It was adapted into a 26-episode, full-length series in 2005-06. Both versions of IGPX were co-productions between Cartoon Network and Japanese animation studio Production I.G. Anyway, the full-length series is sort of a sequel to the microseries, but not really. The microseries was set in 2035, but the new series is set in 2049, and the characters are somewhat different (including their surnames). But the biggest difference is that the original series was basically just teams of mechs battling each other, whereas the new series is teams of mechs racing and battling each other. Three laps on a 60-mile track: one lap of racing, one lap of battling, and the third lap is racing again. I should also say that the races are in 3-D CGI, while the rest of the show is in traditional 2-D animation.

Each team has three racers: a Forward, a Midfielder, and a Defender. This series focuses on Team Satomi, which has just won the IG-2, which makes them eligible to race for the first time in the IG-1 (the highest level of the IGPX). The main characters are the Forward, Takeshi Jin; the Defender, Liz Riccaro; and the Midfielder, Amy Stapleton (both the youngest and the smartest member of the team, Amy synchronizes with her cybernetically enhanced cat, Luca, during races). Takeshi is dedicated to winning, but also doesn't seem to take anything very seriously, so he often clashes with Liz, while Amy tries to make peace as much as possible. Oh, I should also mention that Takeshi has a little sister named Yuri. Other members of Team Satomi include the team's owner, Michiru Satomi; the pilots' coach, Andrei Rublev (about whom a secret is revealed at the end of the first season, though I had guessed it much earlier); a mechanic named Mark Ramsey; and a substitute pilot, River Marque, who's just waiting for his chance. There's also a girl named Jesse Martin, who's like an assistant to Miss Satomi, or something.

Anyway, in each race, two teams compete against each other... Team Satomi's rival teams include Sledge Mamma (an aggressive team which often wins by cheating, whose Forward, Yamma, takes an immediate dislike to Takeshi). River eventually quits Team Satomi and joins Sledge Mamma. And there's an all-female team called Skylark (whose Forward, Fantine Valjean, eventually starts dating Takeshi). The current IGPX champions are Team Velshtein (whose Forward, Cunningham Hume, will be one of Takeshi's toughest rivals). There's Team Black Egg (which concentrates on defense rather than offense). And Team Edgeraid (whose Forward, Bjorn Johanssen, has a cybernetic dog named Sola, who will have a rivalry with Amy's cat Luca).

There are also lots of familiar voices, including Haley Joel Osment as Takeshi, Michelle Rodriguez as Liz, Hynden Walch as Amy, Lance Henriksen as Andrei, Mark Hamill as Yamma, Tom Kenny as sportscaster Benjamin Bright, Steve Blum as Cunningham, etc.

Well, it may be a bit of a spoiler, but I have to say that at the end of the first season, Team Satomi won, so they start the second season as champions rather than rookies. The team to finish in last place drops out of the IG-1 for the next season, and that was Black Egg. They're replaced by Team White Snow (Forward Zanak Strauss; Midfielder Max Erlich; and Defender Judy Highsmith). They also cheat, by hacking their opponents' mechs' operating systems to take control of the mechs during battles. What else to say? We learn that Andrei had a past rivalry with a former teammate of his from his racing days, Sir Hamgra, the current coach of Team Velshtein. And... I guess that's all I can think to say.