I would like to contribute to this great thread.
First of all, I believe tells are player specific for the most part. But some common tells are:
Heavy breathing. You can see the players shoulders rising up and down, you may even hear them breathing hard. Most of the time, this is when someone flops a BIG hand. However, people do this sometimes when they are bluffing.
Trembling hands. You can see this tell easily, as it will be difficult for the player to place his bet because he is so shaky. Not always, but most of the time this tell indicates a big hand or monster draw.
The intimidation tell:
This is more of a general body language tell. This is when a player will try to stare you down or splash the pot very aggressively. It may seem as if they are trying to bully you out of the pot. However, if they had a great hand, why are they trying to make you fold? Many times (but not always), this may be a player who totally missed the flop, but is trying to win the pot.
As with all tells, they are not always accurate, and experienced players may project incorrect tells on purpose (I sure do).
So take this post with a grain of salt. Just my $0.02