Kartoo www.kartoo.com

Kartoo is my personal pick in visual clustering engines category. Being a fan of visual search, I must say that they have a nice flash based layout along with a balanced use of content and display. Once you have reached on some kind of consensus after doing your research on the Kartoo, you might like to preserve your steps/efforts, which went in finding the relevant information. So user-friendly features like: ability to save, load and print your visual map, zoom in and out of the clusters using the clicks comes handy. You don't have to do login and logout stuff for using these features.