Modify / Add to the shortcut buttons when posting

I’m interested in adding to the buttons when writing a post. For example, it would be really nice to have a button for H1,H2, and H3. One for smiley’s would be good too. Most importantly, I have a specific plugin I want to write and it would have some custom code with it as well that I would like to be able to insert with the press of a button.

How do I do that? Must I hack the wordpress code directly or is there a more smooth way?