Here are some I can come up with off the top of my head:
Nadal - butt picking, uses his hand to pin imaginary hair behind each of his ears before each serve, dodges lines when going on the court, calls for the towel after almost every point, sets up his water/other liquid bottles "just so" and is very careful not to disturb the order.
Federer - weird hair toss to get it out of his face.
Djokovic - hands on hips after most errors or a winner from the opponent, bounces ball forever on important points, smiles at random times when returning serve.
Roddick - always cups hat, pulls at shirt (one side, then the other immediately after), hilarious jump/twist when serving.
Sharapova - always straightens strings with her back to the opponent after a point, bounces ball same way with her body in an awkward pose before serving, does some weird toe-heel walk between points.
I'm tired of listing them.
Nadal - butt picking, uses his hand to pin imaginary hair behind each of his ears before each serve, dodges lines when going on the court, calls for the towel after almost every point, sets up his water/other liquid bottles "just so" and is very careful not to disturb the order.
Federer - weird hair toss to get it out of his face.
Djokovic - hands on hips after most errors or a winner from the opponent, bounces ball forever on important points, smiles at random times when returning serve.
Roddick - always cups hat, pulls at shirt (one side, then the other immediately after), hilarious jump/twist when serving.
Sharapova - always straightens strings with her back to the opponent after a point, bounces ball same way with her body in an awkward pose before serving, does some weird toe-heel walk between points.
I'm tired of listing them.