Conditional Moves!
Conditional moves are AWESOME... just don't make them visible to your opponent like several sites do.
maybe some conditional messaging too.. i'll throw in what i think what the next moves will be with some escalating conditional taunting.
1. saw that one coming
2. puuhhhleezee, like that's going to work
3. you see what you make me do!!
4. i'm in your head
5. go ahead go 6.Nxd5, i dare you
6. oh no, you didn't...
7. it puts the lotion in the basket
I also play on another site and really like the "Conditional Moves" feature. It allows you to set up conditional moves that will be triggered automatically in response to specific moves made by your opponent. I use it with obvious 1 or 2 mate moves or capture responses. Very nice time saving feature.