Hmm, mystery margins. Sometimes, it's not easy to pin down exactly which element has extra spacing. To ensure broswer consistency, try a CSS reset:

* { margin:0; padding:0;} 

This will remove the extra margins, but it will also reset the defaults for every element on the entire page. Personally, I like this approach, because I have a finite amount of control over everything and it's usually cross-browser compatible.

There are other alternatives to a browser reset, notably Eric Meyer's reset:
http://meyerweb.com/eric/tools/css/reset/

and YUI Reset CSS:
http://developer.yahoo.com/yui/reset/

Both are a little less disruptive than the star selector, but I like the star for its simplicity. I'm sure our other developers have opinions on this :)