A Truly Vertically Centred Button

Consider the table cell

<td> <!--Adding 'height=100 style="vertical-align:middle"' makes it
easier to view -->
<form>
<input name="button" type=button value=Go>
</form>
</td>

This will produce a cell with a button vertically centred, but visibly
off: the button is being centred by its baseline, not its true centre.
What CSS can be applied to truly make this button vertically centred
(i.e., the space above and below is equal)?

Thanks!