I was looking for some poster advice for a colleague and I stumbled on the following site:

http://www.ncsu.edu/project/posters/NewSite/

I like this site rather well.  It has clear, step by step guidelines for making a poster, as well as links to other poster advice sites.

It also has lots of images of example posters, with thumbs up/down comments for each one.  There is also an example of a poster before/after a friendly critique.

I think you'll find this an interesting and useful resource.

===========

Another resource:

http://www.siam.org/meetings/guidelines/poster.php