One of my pet peeves about CSS and HTML standards is sometimes, they aren't overly explicit, and browser vendors pick arbitrary values for things like line height, or margin or padding and the like.  Eric Meyer has talked about a reset.css stylesheet that would effectively eliminate those differences and override the browsers value with the ones that you know and you specify.

I'm excited to see that he posted a version of it (though reading the comments, it sounds like there will be a few revisions coming) on his blog today.  I'd highly recommend checking it out.  He based it on the one from the guys at Yahoo! UI, added a few things and tweaked a few others.  It's certainly one way to help eliminate those frustrating hair pulling "why isn't this working" kinds of questions!