fluid divs to fill remaining vertical space

Question

I'm messing with a new layout for a site and i've whacked together a form setup, but i'm experimenting with how fluid i can make this new layout. I've got close but no cigar, as the items are floating into position but as you will see in the example below is the item on the right is 400px bigger than the one before it, the next item won't immediately float under the shorter box, it will float at the end point of the longer box on the left side, so you have this big white space that just ruins the look of the layout.

Here is the fiddle: http://jsfiddle.net/xMzb8/

And here is the code for future reference:

HTML

<div class="accountBox">
    <div class="AB-innerFull">
        <p class="AB-title">Registration Form 1</p>
        <div class="AB-innerBody" style="height: 200px;"></div>
    </div>

    <div class="AB-innerHalf">
        <p class="AB-title">Registration Form 2</p>
        <div class="AB-innerBody" style="height: 400px;"></div>
    </div>

    <div class="AB-innerHalf">
        <p class="AB-title">Registration Form 3</p>
        <div class="AB-innerBody" style="height: 122px;"></div>
    </div>

    <div class="AB-innerHalf">
        <p class="AB-title">Registration Form 4</p>
        <div class="AB-innerBody" style="height: 560px;"></div>
    </div>

    <div class="AB-innerHalf">
        <p class="AB-title">Registration Form 5</p>
        <div class="AB-innerBody" style="height: 120px;"></div>
    </div>

    <div class="AB-innerHalf">
        <p class="AB-title">Registration Form 6</p>
        <div class="AB-innerBody" style="height: 50px;"></div>
    </div>

    <div class="AB-innerHalf">
        <p class="AB-title">Registration Form 7</p>
        <div class="AB-innerBody" style="height: 230px;"></div>
    </div>
</div>

CSS

* {
    color: RGB(0, 0, 0);
    font-family: Calibri;
    font-size: 14px;
    list-style: none;
    margin: 0;
    padding: 0;
    text-decoration: none;
}

body{
    padding: 5px;
}

.accountBox {
    background: RGBA(200, 230, 240, 0.6);
    border: 1px solid RGB(20, 100, 150);
    float: left;
    margin: 10px 29px;
    padding: 5px;
    width: 870px;
}

.AB-innerHalf, .AB-innerFull {
    background: RGB(255, 255, 255);
    border: 1px solid RGB(200, 200, 200);
    box-shadow: 0px 0px 2px RGB(220, 220, 220);
    box-sizing: border-box;
        -moz-box-sizing: border-box;
    float: left;
    margin: 5px;
    padding: 40px 20px 20px;
    position: relative;
}

.AB-innerHalf {
    width: 425px;
}

.AB-innerFull {
    clear: left;
    width: 860px;
}

.AB-innerBody {
    background: RGB(255, 0, 0);
    clear: left;
    float: left;
    width: 100%;
}

.AB-title {
    border-bottom: 2px dotted RGB(20, 100, 150);
    color: RGB(20, 100, 150);
    font-size: 16px;
    font-weight: bold;
    height: 25px;
    left: 0;
    line-height: 25px;
    margin: 5px 10px;
    padding: 0 5px;
    position: absolute;
    text-transform: uppercase;
    top: 0;
}

Answer 1

give flot: right to the bigger box

  <div class="AB-innerHalf" style="float:right">
    <p class="AB-title">Registration Form 4</p>
    <div class="AB-innerBody" style="height: 560px;"></div>
</div>

Answer 2

May be,
this could solve your problems...!?

http://isotope.metafizzy.co/