This subject crops up from time to time. I'm always surprised to see other people's ideas. It all depends on your definition of ugliness I suppose. I've seen a lot of aircraft of all shapes & sizes over the years but can't say I would call any of them ugly. Interesting or unusual might be better descriptions. There is usually a very good reason for the way they look. Something that appears ugly at first sight will often become attractive or even beautiful the more you see of it. I thought the Boeing 747 looked very odd the first time I saw one.

Here's one example of an aircraft only a mother or designer could love. The Farman F-4X Jabiru. This is the only photo I've ever seen of it. I can only suppose that there is an open cockpit on top of the fuselage. http://www.simviation.com/yabbuploads/113684.jpg

The Jabiru could carry 6 passengers. Four examples were built & actually entered service in 1925.