Any suggestions for subgames?

How about:
Rock paper scissor
Radio scan-turn a radio onto scan, players try to be the first to name the artist and song as it scans from one station to the next. Most named wins after one complete scan.
Cup stack or whatever its called. Each player must stack plastic cups into a pyramid then disassemble. Fastest wins..
Shell game
Quarters
Asian dice game-cant remember its name. Players lay wagers on a mat coresponding to different sides of a die(they use animals and such).3 dice are rolled. If you bet $5 you win $5 if one die matched,$10 if two match,$15 if all three match

Poker flick! Basically Texas Hold 'Em with a dexterity element. Try to assemble a winning poker hand by flicking disks onto a number of cards spread out on the table. Best hand wins. Possibly begin by dealing out a starting hand to players.

Card roulette Bets can be on suits, even/odd/face, color, or specific cards. Joker gives everyone their money back plus a small bonus. You'd need a chart of course, but that's an easy print job. Once bets are placed, flip over a card and pay out to any winners.

There was a game like that published here in quebec called "Pari-Mani". Which could be translated as "Bidding-Mania". The BGG entry is here:

http://www.boardgamegeek.com/boardgame/20444/pari-manie

It is a roll and move game where you can land on spaces where you can play casino games.

There is a small card for every game that tells you how much your initial bid is multiplied if you win. So all the games you play are against the game (the dealer can be another player).

So if you look at this picture

http://www.boardgamegeek.com/image/104307/pari-manie?size=original

You can see the payoff charts. Black jack is the only one we can clearly see. It read as:

> 21 = lose your bid
< 17 = take a card
17 = keep your bid
18, 19 = gain 1 x bid
20 = gain 2 x bid
21 = gain 3 x bid
black jack = Gain 5 x bid
<21 in 5 cards = gain 7 x bid
7,7,7 = gain 10 x bid

So you have a payoff card for every game. You have 4 games at the corner plus the slot machines which is done with colored dices and horse races done with a small stack of cards.

I don't know if it helps, it could be a good source of ideas. If you need help for the translation of the picture on BGG from french to english, let me know.

I once threw together an incredibly simple gambling game for an upscale inn in one of my D&D campaigns. There's a lot of fluff attached, but enjoy nonetheless.

1 B: Zares’ Gambit
The formerly obscured portion of the room, a large area closed off by countertops marked with shapes and colors, appears to be set aside for a game of chance that involves betting on various numbers and color. These elements of chance appear on a wheel and a die, respectively. Two employees, one rolling a die and collecting bets, the other the wheel, man this station.

A DC 15 Knowledge (Local), (History), or a Bardic Knowledge check will recall that this game, affectionately referred to as Zares’ Gambit, is a game of chance in which a wheel with sets of three numbers ranging from one to six on each of its spokes and a three-colored die that randomly selects a color are used. Betting can be made on the numbers that appear on the wheel, the colors on the dice, or that a color AND a number will appear on the same roll, offering a chance for players of various levels of logic and skill to come together and play the same game. This is a fitting game to bear Zares’ name, as his rallying call was one of equality.

The Riverfront allows betting on any number of numbers or any number of colors per round of betting. If a better bets both on a color and a number, they cannot win separately and that player can only select one number and one color.

The betting range accepted at The Riverfront is 1s to 10g per number or color.

Odds:
Number pays 2:1 for each match on the board
Color pays 1.5:1
Number and Color pays 5:1

To play:
Roll 3d6 for the numbers
Roll 1d6 for color

D6
1-2: Red
3-4: Blue
5-6: Yellow