text-indent: -999em; /* Hide the text, works in most modern browsers */

/* --- Needed for IE --- */
font-size: 0px; /* works well in IE7. still a black line (basically the text) in IE6. */

display: block; /* Negative text-indent works in IE(6? worked fine in 7) only if this is added. */

line-height: 0px; /* Another fix for IE6. */

text-indent: -999em; /* Hide the text, works in most modern browsers */

/* --- Needed for IE --- */
font-size: 0px; /* used to reduce the font size and works well in IE7. But even after adding this line, you would notice a black line(which is basically the text) on the center of the button in IE6. */

display: block; /* Negative text-indent works in IE(6? worked fine in 7) only if this is added. */

line-height: 0px; /* Another fix for IE6. */

Hide text on input[type=submit]

CSS