When working on your research poster, start with these judging criteria in mind. Those should guide your design decisions, based on the content you have to support them.
Here are some helpful poster design sites:
Swarthmore College This site includes a poster gallery on Flickr and various other visual examples, plus numerous handy links. I also like the irreverent voice in which the author writes about the poster sharing process.
University of Buffalo site has many links and a straightforward explanation of the process.
The Cain Project, at Rice University, also is well done.
Here are a few recommended by the WSUV Research Showcase site (although I'm not as excited about these):
"Creating Effective Poster Presentations: An Effective Poster."
by George Hess, Kathryn Tosney, and Leon Liegel
A fairly detailed discussion about what a poster is meant to do and how to go about developing one.
"Communicating Your Research and Results Through a Poster Presentation."
by Duke University's Visible Thinking
An extremely effective discussion about creating posters, with examples and terrific suggestions. Practices what it preaches!
"Creating Posters for Humanities & Social Sciences."
by College of Arts and Sciences at Eastern Oregon University
Another looks at developing posters, but specifically aimed at humanities and social sciences scholars. Web design is circa 1996.