If you liked the Liar Game manga, the Anime-Planet community thinks you'd like:
Both involve games that gamble huge sums of money and pivot around mental games that invlolve looking into opponents minds and figuring out the best way to defeat them. The main characters in both are also the few people who are righteous/just among all the other people who succumb to greed.
Kojima is a baseball legend. As the superstar cleanup hitter for the Lycaons, he won himself many awards including rookie of the year seven times; but there's one title he never acquired: champion. In an attempt to find that special something Kojima feels he's missing inside, he opens a training camp in Okinawa. There, through a series of events, Kojima is introduced to a high stakes game dominated by the talented Toua Tokuchi, and subsequently loses a fortune. However, Kojima finally defeats Toua and due to their agreement, he enlists him to join the now poorly-ranked Lycaons - but Toua demands a high price: instead of a salary, he will receive five million yen for each out, and lose fifty million yen for each point lost. With a bad attitude and prodigal skills, Toua will help transform the Lycaons into winners once more.
The same author and pretty much the same feeling. Devilishly intelligent genius who is stepping on a thin line between crime and legal outwits all of his oponents. The only difference is the stage they are fighitng for - in One outs it's baseball, in Liars game it's different sort of gambling games.
Itou Kaiji is as pathetic a person as they come; a man who gambles his days away, only winning enough to lose significantly more. He hates himself, is riddled with envy for others, but is ultimately too weak to think of a way out of his massive debts. Then one day he is approached by a strange man who offers him what seems the solution of a lifetime – to take a short journey on a ship called Espoir, during which time he will be given the chance to win more cash than he can dream of in a card game like no other. Ever the desperate, Kaiji takes the gamble of his life; however, the game turns out to be far darker than he expected and the hard lessons pile on thick and fast. Now stuck in a closed world of unsavory characters willing to do anything to destroy him, can Kaiji gather enough courage to outwit them all?
Both manga involve a shady organization that "charitably" gives people in debt an opportunity to erase their debt at the risk of taking on even more debt that they would never be able to possibly pay off in their lifetime. The main characters are both very intelligent individuals that tested game after game by various devastating high stake games. If you enjoy one you will most definitely enjoy the other. The only main difference between the two is the characters and their motives
Both mangas feature a clever protagonist and a not-so-good one with hidden potential and both feature various challenges/games, which the protagonists must overcome in order to achieve their goals. Liar Game is psychological and realistic, ToG is a fantasy, but if you like either one there's a strong change you'll the other one as well.
The psychological/thriller mangas Liar Game and Shi ga Futari wo Wakatsu Mada (aka Until Death Do Us Part) each have dark overtones with similar themes and charismatic, unforgettable characters.