Since your entering as html in a text widget, give them a class of widget-4
or such.
You can then use css.
Here's an example:
<div class="widget-4"><a href="http://www.thenichemommy.com/" target="blank"><img border="0" src="http://www.thenichemommy.com/wp-content/uploads/2013/09/Niche_Parent_Member_Badge.png"></a></div>
That way you can leave out the <center> tags & inline styling.
Use css in your stylsheet:
widget-4 {
float: left;
}