Kingdom Rush - The Dark Tower Normal Campaign Eight Towers Singleton Challenge by nsscclerk, on Flickr
Non-premium, using only each of the eight tier 4 towers with all specials maximally skilled, Rain of Fire and Call Reinforcements.
Link to the video
http://youtu.be/ZhKQOskS1lI
Thanks to Epicazeroth for the suggestion.
What about this? I usually try to do it this way: only eight towers, one of each advanced (one big Bertha, one tesla, one paladins, one rangers, etc.)