As usual, when it came time for me to make a poster for a conference, I wanted something that fit into my normal work-flow (cvs, LaTeX, and lots of eps files with a nice pdf at the end). I ended up taking an existing set of poster macros and modifying to my liking. This mostly involved combining different files and changing separate packages into options for a unified package. I have used this mostly for horizontal posters (of more or less A0 size), so the vertical options are not as well tested. The "mini" amd "maxi" options to the poster class determine large format or small (8.5X11) format output, allowing you to easily switch the size of you poster for use on normal printers (for handouts, or just to see how it looks). There is a sample file that provides the skeleton of a poster included. It would probably be best to start with that and fill in your own stuff there.
The one major catch to this is that the body of the poster is implemented as a picture region, so extra blank lines in each column are NOT IGNORED as they normally are in LaTeX. This is the causes of lots of errors.
It is of course best if make a pdf of your poster since anyone who is capable of printing a large format poster should be capable of printing a pdf. You might want my LaTeX Makefile to automate this.
I hope to make some additional updates to this soon, but since I don't have any posters coming up soon, I'm not sure when that will happen.
The LaTeX macros here are descendants of Poster macros from Brian C. Wolven.
I intend to put some LaTeX files for making a poster up here, but since they require some directions, I don't want to just throw them up there. But for now, there is still some useful info I can give. The information below is mostly University of Maryland specific at the moment.
First, you should make your poster nice and official looking with the university logo at the top. Go to this page for University of Maryland logos. If you bother to read through everything, you will see that you need the informal logo. LaTeX users should use the encapsulated postscript (eps) file offered. OpenOffice.org users can uses either and just use ImageMagick's convert routine to make a png to insert. Powerpoint users on OS X can do the same. Powerpoint users on Windows probably need to find a good computer with convert on it (or photoshop I guess) to make a png out of the tiff file.
For actual printing, the Physics Copy Center in Room 1213 of the Physics Building was very good when I used them. Very fast (took about an hour for me, but you really cannot count on that fast) and cheap. Spend the extra $10 or so on vinyl printing. It gives you a much sturdier poster which looks good, and is easier to handle. It does smell a little bit like vinyl, but that goes away after a week or so. Total cost was around $60 for an A0-ish (46.6x36 inches) (which is about one third the cost of Kinko's).