Best single IE6 CSS cheat for 90% of my problems:

  zoom:1

Learn it, love it, use it.

It makes IE use its old renderer calculations (hasLayout) for whatever element you put it on, so it often fixes disappearing items, incorrect overflow, floats, padding/spacing etc. If your style looks correct in other browsers, give zoom:1 a shot on IE6 and see if it fixes things before wasting another minute.

ps. For those that are validation crazy, there are other triggers for hasLayout that will validate (certain padding, margins, etc.) but they vary from element to element, whether they have ancestors, etc. and you'll waste a great deal of time figuring them out.