I do a Recent Photos module on our blogs
(example) that makes all the thumbnails 120 pixels wide. This gets a little funky when the original images are very long and narrow, or shallow and wide, but it usually works pretty well.
If your images all start square, they'd end up square, but I'd hate to distort horizontals and verticals to that shape.
Here's what does it:
CODE
<mt:IfNonZero tag="AssetCount">
<mt:Assets type="image" lastn="3"><br />
<mt:AssetsHeader>
<div class="widget-content">
</mt:AssetsHeader>
<ul style="padding:0; margin:8px 0;>
<li style="padding:0; margin:8px 0; list-style-type: none; align: left; border: 2px; "><a class="asset-image" href="<$mt:AssetURL$>"><img src="<$mt:AssetThumbnailURL width="120"$>" class="asset-img-thumb" alt="<$mt:AssetLabel$>" title="<$mt:AssetLabel$>" /></a></li>
<mt:AssetsFooter>
</ul>
</div>
</mt:AssetsFooter>
</mt:Assets>
</mt:IfNonZero>
<mt:If tag="AssetCount" gt="5"><a href="<$MTBlogUrl$>photos.html"><em>More...</em></a></mt:If>