Awesome thread and I thought I'd share one tip that's helped get my layouts look the same with IE and Firefox. When creating a stylesheet I type it out adhering to CSS2 standards and it always works out fine with Firefox but when viewing it in IE sometimes there is the odd div that isn't positioned exactly the same so I create an extra rule for IE only by adding !ie:
#wrapper {
top: 0px;
top: 5px !ie;
}
In this example the div snuggles up to the top nicely with Firefox but with IE it was nudged up slightly higher so I added a little padding that Firefox ignores but IE reads.
