How many times has this happened to you? You hit top pair, top kicker on the flop. You make a pot-sized bet to protect against any flush and straight draws on the board but still get one caller. Naturally, you put your opponent on a drawing hand. The turn is a brick, and you make another bet. You get another quick call. This guy just won't go away, and now you're absolutely sure he is drawing to a flush or straight. What happens next? Of course, a scare card spikes on the river, and your opponent pushes the all-in button in 0.1 seconds.

"Is that a tell?" you think.

Of course it is, but most players make the mistake of believing their opponent made their hand, and they fold without thinking it through. However, this is the time to pick off the bluff, because most times, if your opponent has made their hand on the river, they will take longer to act because they are trying to decide on a value bet to extract chips. In the example above, you almost always are pot committed and must make the call anyway.
 
Remember that, typically, a quick bet (especially an over-bet of the pot or an all-in) usually is a sign of weakness, while the delayed response or a long 10-second pause is often a sure sign of a monster hand. Instead of agonizing over a value bet, try the instant all-in yourself the next few times you make a hand on the turn or river, and you'll be surprised by how many times your opponent calls, all because of the speed of your action and not the size of the bet. And if you're really lucky, your opponent will recognize a pot-committed call when he sees one and pay you off anyway.

Other Tells
 
The Chat Brat:

There are always players who sit at the table and chat. Most times, of course, the chat takes a turn toward the juvenile side after a bad beat. These players can fall into many different categories. A tilting player is easy to spot as they often tend to become abusive and insult everyone. Chatty players who suddenly go quiet might have flopped a good hand, so be alert.
 
Check/Box Button: When it is folded to a player and he instantaneously checks, this usually means he has pressed the check/fold box. Usually a bet here will win you the pot. Rarely is an opponent savvy enough to check-raise here if they have pressed the check/fold box.
 
Instant Raise/Bet (limit): If a player makes a bet on the end and another player raises instantaneously, it's obvious that he has pressed the Raise Any button. This shows that the player has a very strong hand.
 
Delayed Check: Players who take their time to check usually have missed their draw or have a very weak hand and are trying to represent strength by taking their time. This is also done to try and see the next card for free.
 
Hand History: This is not so much a tell, but in online poker you can request every hand you played. From this you can see the action that took place from the last hand. Any hand in online poker that has been called at the end will show the winning hand and not often the losing hand. This is a very powerful tool to see how a person bets with particular hands, if he chases flush draws, etc. From this, you can make notes on players on how they play, so you can judge what type of player they are.

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