My TikZ poster
NOTE that we joined our efforts with the tikzposter team, which resulted in an improved version 2.0 of the tikzposter class that you can find in http://www.ctan.org/pkg/tikzposter. This class combines both good structure and nice layouts. The official webpage of our project is https://bitbucket.org/surmann/tikzposter/wiki/ (under construction).
I am not going to maintain this style.
I was to prepare my first scientific poster (for KR 2012) and tried to look up the existing solutions. I did not like Beamer poster, and since I was already quite familiar with TikZ and knew what one can do with it, I have decided to create my own style based on a0poster and TikZ only, and called it fancytikzposter. Then I got into it so much that I developed different poster templates with the possibility of personalizing the look of the poster. See my posters here and here.
If you want to make a poster using my template, download fancytikzposter sources and pdf with instructions (that can be also obtained by compiling the source files):
By now, there are five templates with different node shapes and colors.
UPDATE. June 25, 2013. The current version is 2.1. I added a sixth template, a variation of the 3rd template, it is not very serious, but I like how it looks. Though I am not sure it can be really used for a scientific poster. I also did some minor changes: added an environment for figures as the standard figure environment does not work inside a tikzpicture. Now you can use the tikzfigure environment (thanks to Stephan Thober for a first version of it), it does not provide the full functionality of the figure environment, but it has counters and optional captions. I also renamed some macros (sorry for that) to have a bit more coherent naming of the various blocks. The version 2.0 can be found using this link.