You wouldn't necessarily need any plugins for that. You can modify the index page to not display anything but an image (which would be a custom field, ideally) for each post. So basically just take out anything inside of the loop except for the thumbnail, then format the thumbs to float to the left and give them a width so that they wrap into new lines.
1. modify index.php
Replace all stuff in there with this:
Code:
<?php if(have_posts()) : ?>
<div id="content">
<?php while(have_posts()) : the_post(); ?>
<div class="thumb">
<?php $values = get_post_custom_values('thumb');
echo get_post_meta($post->ID, $values[0], true); ?>
</div>
<?php //loop ends
endwhile; ?>
<div class="clear"></div>
</div> <!--close content-->
<?php endif; ?>
Custom fields at wordpress.org:
Using Custom Fields WordPress Codex
The above fetches a custom field with the key "thumb" from the post. That field must contain the attachment ID of the uploaded image you want to use as a thumb.
To do this:
a) upload an image in the post as usual
b) do not insert it into the post, but note its ID number
c) add a new custom field to the post with the keyname "thumb" and a value of its ID number.
2)
Now you need to just float the div.thumb in the code above to the left and add some padding/margin. Also advisable is to give it a fixed size and limit the size of the thumbs in your CSS as well. You could do this:
Code:
.thumb { width:200px; height:200px; float:left; padding:5px; border:1px solid #ccc; margin:0 10px 10px 0; overflow:hidden; }
.thumb img { width:200px; }
Only give the contained image either a width or a height, not both, in order to keep the width/height ratio.
I haven't tested this particular code, but it should work and I hope it helps.