<ul class="flexcontainer">
    <li>Something</li>
    <li>Fox Example</li>
    <li>All About Web</li>
    <li>Fox Example</li>
    <li>Something</li>
    <li>Fox Example</li>
    <li>Something</li>
    <li>Fox Example</li>
</ul>

.flexcontainer {
    width: 300px;
    display: flex;
    flex-flow: row wrap;
}
.flexcontainer li {
    width: 50%;
    background-color: pink;
}

http://jsfiddle.net/bdm5d8p4/

关于flexbox可以参考这篇文章：http://segmentfault.com/a/1190000002910324.