Index: wp-admin/includes/media.php
===================================================================
--- wp-admin/includes/media.php	(revision 18444)
+++ wp-admin/includes/media.php	(working copy)
@@ -1851,6 +1851,22 @@
 	<tr>
 	<th scope="row" class="label">
 		<label>
+		<span class="alignleft"><?php _e('Size:'); ?></span>
+		</label>
+	</th>
+	<td class="field">
+		<select id="size" name="size">
+			<option value="thumbnail" selected="selected"><?php _e('Thumbnail'); ?></option>
+			<option value="medium"><?php _e('Medium'); ?></option>
+			<option value="large"><?php _e('Large'); ?></option>
+			<option value="full"><?php _e('Full'); ?></option>
+		</select>
+	</td>
+	</tr>
+
+	<tr>
+	<th scope="row" class="label">
+		<label>
 		<span class="alignleft"><?php _e('Order images by:'); ?></span>
 		</label>
 	</th>
Index: wp-admin/js/gallery.dev.js
===================================================================
--- wp-admin/js/gallery.dev.js	(revision 18444)
+++ wp-admin/js/gallery.dev.js	(working copy)
@@ -111,7 +111,7 @@
 	},
 
 	setup : function() {
-		var t = this, a, ed = t.editor, g, columns, link, order, orderby;
+		var t = this, a, ed = t.editor, g, columns, link, order, orderby, size;
 		if ( ! t.mcemode ) return;
 
 		t.el = ed.selection.getNode();
@@ -124,6 +124,7 @@
 				if ( getUserSetting('galdesc') == '1' ) t.I('order-desc').checked = "checked";
 				if ( getUserSetting('galcols') ) t.I('columns').value = getUserSetting('galcols');
 				if ( getUserSetting('galord') ) t.I('orderby').value = getUserSetting('galord');
+				if ( getUserSetting('galsize') ) t.I('size').value = getUserSetting('galsize');
 				jQuery('#insert-gallery').show();
 				return;
 			}
@@ -140,11 +141,13 @@
 			link = a.match(/link=['"]([^'"]+)['"]/i);
 			order = a.match(/order=['"]([^'"]+)['"]/i);
 			orderby = a.match(/orderby=['"]([^'"]+)['"]/i);
+			size = a.match(/size=['"]([^'"]+)['"]/i);
 
 			if ( link && link[1] ) t.I('linkto-file').checked = "checked";
 			if ( order && order[1] ) t.I('order-desc').checked = "checked";
 			if ( columns && columns[1] ) t.I('columns').value = ''+columns[1];
 			if ( orderby && orderby[1] ) t.I('orderby').value = orderby[1];
+			if ( size && size[1] ) t.I('size').value = size[1];
 		} else {
 			jQuery('#insert-gallery').show();
 		}
@@ -162,7 +165,7 @@
 		if (t.el.nodeName != 'IMG') return;
 
 		all = ed.dom.decode(ed.dom.getAttrib(t.el, 'title'));
-		all = all.replace(/\s*(order|link|columns|orderby)=['"]([^'"]+)['"]/gi, '');
+		all = all.replace(/\s*(order|link|columns|orderby|size)=['"]([^'"]+)['"]/gi, '');
 		all += t.getSettings();
 
 		ed.dom.setAttrib(t.el, 'title', all);
@@ -192,6 +195,11 @@
 			setUserSetting('galord', I('orderby').value);
 		}
 
+		if ( I('size').value != 'thumbnail' ) {
+			s += ' size="'+I('size').value+'"';
+			setUserSetting('galsize', I('size').value);
+		}
+
 		return s;
 	}
 };