Explicitly exclude an html element from the tab order

Is there any way to exclude an element from the tab order of a HTML form.

So if i have the following

<input type=text name=username>
<input type=text name=password>
<input type=button name=forgotpassword>
<input type=submit name=login>

I'm aware that I can use tabindex as 1,2,3,4 but i don't want to have to number all the fields. My application is dynamically creating the fields.