Vertically aligning a checkbox

Vertical alignment only works on inline elements. If you float it, then I don't think it is treated as part of that stream of inline elements any more.

Make the label an inline-block, and use vertical alignment on both the label and the input to align their middles. Then, assuming it is okay to have a specific width on the labels and checkboxes, use relative positioning instead of floating to swap them (jsFiddle demo):

input {
    width: 20px;

    position: relative;
    left: 200px;

    vertical-align: middle;
}

label {  
    width: 200px;

    position: relative;
    left: -20px;

    display: inline-block;
    vertical-align: middle;
}

Its not a perfect solution, but a good workaround.

You need to assign your elements to behave as table with display: table-cell

Solution: ^Demo

HTML:

<ul>        
    <li>
        <div><input type="checkbox" value="1" name="test[]" id="myid1"></div>
        <div><label for="myid1">label1</label></div>
    </li>
    <li>
        <div><input type="checkbox" value="2" name="test[]" id="myid2"></div>
        <div><label for="myid2">label2</label></div>
    </li>
</ul>

CSS:

li div { display: table-cell; vertical-align: middle; }