Since this is a menu, might as well take it to the next level, and clean up the HTML, and make it more semantic by using a list element:
HTML:
<ul id="menu">
<li><a href="#">Bla</a></li>
<li><a href="#">Bla</a></li>
<li><a href="#">Bla</a></li>
</ul>
CSS:
#menu {
margin: 0;
}
#menu li {
float: left;
list-style: none;
margin: 0;
}
#menu li a {
display: block;
line-height:30px;
width:100px;
background-color:#000;
}
#menu li a:hover {
background-color:#F00;
}