I wrote a post about how to view/filter multiple labels at one time back in Nov 2011, but that technique no longer works.
Here is an updated technique, which does work at this point in time.
Search multiple labels
Lets say you want to display all post entries on this blog that have the labels "Blog" and "HTML".
The URL will be this:
http://geekstuff.allnewadventures.com/search/label/Blog+HTML
Or simply
http://BLOG-ADDRESS/search/label/LABELNAME1+LABELNAME2
It's the plus sign (+) that makes all the difference :-)
NOTE: BLOG-ADDRESS is your full address such as http://blogname.blogspot.com or if you have your own domain then http://yourdomain.com
Did you find this information useful? I'd love to hear your feedback, so please leave a comment if this post was helpful to you.