This page lists a critique of the loyalty systems of different online poker rooms.
888 Poker offers their players an okay loyalty program. For every $10 placed in bets, Pacific Poker awards players 1 bonus point. Every 100 points may be converted into $1 in cash, so every $1000 placed in bets gets you $1 back in cash.
Party Poker offers their players a frequent player points program. They also offer their players redeposit bonuses of 15%-25% up to $100 on a random basis, depending on how often the player is playing.
Hollywood Poker offers their players a loyalty system, but did not provide many details on their website. The points can be used for tournament buy-ins or to pay for Hollywood Poker merchandise. Hollywood Poker does boast a 500% bonus up to $1,000 and it must be released by playing many raked hands at their site. For instance, a player will deposit $200 and $1000 will be available to them in their bonus account, but the money cannot be used until the player has earned it by playing many raked hands.