Finding a printer when you only occasionally need one can be daunting so how great is it that if you can get to Varick Street just west of Soho you will have found a solution to almost all of your printing needs. You can get everything from posters, and I mean big posters, to postcards and even woven wall hangings made from your digital files. The people behind the counter are very friendly and helpful and the prices aren't bad at all if you have gone other places. One day a week, Wednesday, they are trying out a 24 hour turn around time on postcards.
Their website: http://www.dig-ink.com