No Spacer gifs
Besides something that is limited and antiquated, what is a spacer gif? Wikipedia defines a spacer gif as:
a transparent image, often used to control blank space within a web page, that can be resized according to the width and height dimensions it is given. Spacer GIFs are not browser specific. The reason a spacer GIF is invisible is so that an HTML developer can create a table cell and fill the background with a specific color that can be viewed through the transparent spacer GIF.
Although it served a purpose prior to CSS, spacer gifs are no longer necessary. Background colors can now be defined by using the "background" property in CSS. Spacer gifs bloat up a web page by adding additional junk markup to the already enormous volume of junk markup found within table-based layouts. Consider also what your page would look like if a visitor were to have images disabled. Other than that, there isn't much else to say about spacer GIFs. Don't use them.
Accept no substitutes - migrate to CSS, and
"Just say "NO" to table-based designs!".