Casino and poker apps have been some of the most popular since the launch of the iPhone - one of the very first apps ever developed was Apple Texas Hold'em.
1) Zynga Poker: With more than 30 million active players around the globe, it's hard to top Zynga Poker as far as the selection of games it offers. Featuring a format and gameplay very similar to what you'll find at Internet poker sites, Zynga Poker also is tightly integrated with Facebook, making it easy to invite friends to play and show off the huge stacks of chips you've won.
2) All Slots Casino: The iPhone app from All Slots Casino lets players enjoy many of the same great games as they'll find on the All Slots site, including the chance to chase some big progressive jackpots at slot games such as Mega Moolah and Major Millions.
3) bwin: bwin was one of the first online gambling sites to get an app approved for iPhone users to play for real money (although that function is only available to users in France, the UK, and Austria), offering the chance to bet on sports as well as to enjoy casino and poker games on their iPhones.
4) Apple Texas Hold'em: This one may be the granddaddy of the iPhone poker apps but it's still very popular, and for good reason. Apple Texas Hold'em lets you quickly jump into a game against a variety of computer opponents, each with their own betting tendencies and tells that you'll need to identify if you want to take all their chips away from them.
5) #1 Reel Deal Slots Club: Unlike other slots apps that just let you spin the reels at a few games, #1 Reel Deal Slots Club lets you pay slot machines, fruit machines, and poker machines with detailed statistics available as well as tournaments and other competitions that you can invite friends to play alongside with you.