You name any game and an online version of that game is available. All the games are conducted in controlled and regulated environment. Most games are legal in many countries, while some countries do not allow the games with real money to be played. From horse racing to sports betting and casino games like slots and blackjack everything is available.
Some of the most popular games are:
Blackjack is one of the easiest games to play and has the best odds of winning. Most casinos have very low edge in this game.
Poker is meant for experienced players. A new player will find it difficult to win so he should learn the tricks first before entering the arena.
Crap involves a player against a dice so chances of winning are almost equal.
Roulette wheel is a simple and easy game. Players bet money on a number and colour combination.