Forum Moderators: not2easy
If list-based: the vertical-align property, as I'm sure you know, doesn't work with list items. This is because vertical-align works only to center the contents of a table cell or an inline box. If you've used the height property to set the button height, this acts upon the block level anchor, not the inline text box the anchor contains.
Instead of height, try line-height. This sets the height of the inline text box the anchor contains to match the button image height. Vertical-align should then center to the middle of that (and it should do it by default, since middle is vertical-aligns default setting).
cEM