The way in which I've played amongst friends (based in principle on the game described in Apsrin's Myth series) was to play normal 5 card stud. Then, every fifth hand in which the hand was played out to the end (two players min.), the lowest hand would create a single rule involving a conditional and a change, that made someone other than the current winner into the actual winner. Rules were maintained throughout play, and cumulative throughout the campaign/continent. We even assigned someone to write down the rules, so over time there were a couple of small notepads filled with a series of rules.
Example: On the fifth hand, Rollo, Krieger and Polare are playing in the Kingdom of Andar. Rollo throws up three aces, a jack and a deuce. Polare shows a club straight, 2-6. Krieger shows two pairs, deuces and eights, with an ace. Krieger, as the loser, must now make up a rule about why Polare isn't the winner. He decides that when an ace is the odd card in a two pair hand, it becomes wild. With this rule, his hand becomes the winner with a full house. From then on, all Dragon Poker games in Andar are supposed to be played with this rule.
I've seen a number of people who essentially play some variation on "Between the Sheets/High-Low" and call that Dragon Poker as well. Here's the version that won my gypsy character his first noble title:
Everyone antes some amount. In turn, each player would then add an additional ante and flip two cards. If the first card was an Ace, the player had the option of playing it high or low. The second card, if an Ace, was always high. The player could then bid an amount equal to the ante, up to half of the entire pot, bidding on whether or not a third card would lay between the first two in value. If you wish to "surrender", you may pay half of the value of the ante and pass. If the card does lay between the other two, the players wins his bet. If the card lays outside the other two, the player loses his bet to the pot. If the card is equal to either of the two "sheets", he loses double his bet to the pot. Play then passes to his left. If a full round play has been lost or surrendered to the pot, then players may bid up to the entirety of the pot (with the same double-stakes if you hit the sheet). Because the pot can quickly outstrip someone's ability to bid, some characters have been known to allow bidding "minutes of service".
Example: Gregor, Lorelei, and Duke Brimstone are playing. In the pot is twenty gold, and 12 minutes of service from Lorelei. All three have played a hand and lost or surrendered to the pot, so now bidding is allowed up to the full value of the pot. Duke Brimstone throws in his 1 gold ante, and flips a card: eight. He then flips an Ace (which, being the second card, is played as high). He bids the entire pot: 20 gold and 12 minutes of service. His next card is an eight, so now he must pay in double his bid, totaling the pot to 63 gold, 24 minutes of service from Duke Brimstone, and 12 minutes of service from Lorelei. Lorelei plays next, adding 1 minute of service as her ante, and flips an Ace. She chooses to play it low. She then flips a second ace, which is automatically high. She bids the entire pot, and stunningly, flips a third ace. The pot is now at 63 gold, 24 minutes of service from Duke Brimstone, and 113 minutes from Lorelei. Gregor is now up. He flips a nine and then a seven. He then bids the entire pot, much to the surprise of his companions. Turning over an eight, he now has secured the short-term servitude of a Duke, and a lovely date with a wonderful companion. The fact that he was dealing the cards is entirely and utterly coincidental and any suggestion otherwise is completely without merit.