<textarea id='text'></textarea>
<br>
<select id='cons' onchange='func(this)'>
<option value=''>согласные</option>
<option value='b'>b</option>
<option value='c'>c</option>
</select>
<select id='vow' onchange='func(this)'>
<option value=''>гласные</option>
<option value='a'>a</option>
<option value='o'>o</option>
</select>
<script type="text/javascript">
var kb = {
area: document.getElementById('text')
};
function func(select) {
kb.area.value += select.value;
select.selectedIndex = 0;
}
</script>