The way we most commonly play Anaconda is as a game: we do all the passing before any betting, and then we bet as we roll the cards. An alternative is to bet after the deal and after each pass; this can make for much poorer hands, as people tend to fold and take large chunks of the deck with them.
Passing is usually always to the player on your left; a variation is to make the first pass to the player on your left, the second pass to the player on his left (two away from you), and so on. This variant, too, tends to lower the quality of the winning hands, as you are receiving cards from different people every time: One pass may give you the discards of someone going high, while the next gives you the discards of someone going low, and so on.
A new Anaconda variation is Something Better. (This is yet another game that started as a name and had a game added later.) This is just like normal roll 'em Anaconda, except that it's played as a game - after the last passing round, everyone selects their best five card hand, then reveals one card at a time.
Surreal Poker is a 'straight highball' variant with wild cards. The dealer deals three extra cards, two down and one up. After the first pass, but before the second bet, he turns up one of the down cards. After the second pass, but before the final bet, he turns up the remaining card. The card that's numerically in the middle is wild. Aces are high, and if a pair comes up, it's wild. Thus, if the cards are a two, a five, and a Queen, fives are wild; if the cards are a Jack, a six, and a Jack, Jacks are wild.
Each player gets five cards down, and five common cards are dealt face down in a line. One is turned up, and anyone who'd like it bids on it, typically starting at a nickel. The high bidder pays the pot; takes the card; and then replaces it, face down, with one from his hand. Then the next card is turned up, and bidding starts. If no one wants a card, it's "dead" and is moved, face up, to a different row. When the last card has been bid on, the first discarded card is turned over and bid on. Bidding continues until there are five dead cards, at which point everyone arranges their hand, and plays it as a game.
Junkyard is a less-popular variant. Everyone is dealt five (or seven) cards down. They discard any or all of the cards that they don't want, face down in the center. The discards are mixed up a bit, then arranged in rows of five. The first row is turned face up, and bidding goes from the dealer's left to the dealer's right; when all the cards have died or been bought, the next row is flipped, and so on. It's also played as a game. You don't have to have a five card hand to go high, but you do have to have at least five cards to go low.