I want to create a postcard with LaTeX, say 3x5 or 4x6 in. I use LaTeX for many things, but up to now I've used MS Word for postcards. Now I'd like to do more interesting things with postcards that would leverage LaTeX's capabilities. Where should I start? Is there already a package, or a simple setting, that will do the trick?
Simply use the geometry package to change the page size of your document.
I used LaTeX to create my own wedding reception invitations and RSVP cards using the article class, the geometry package, some parboxes, and a flowerly-looking font. The result was very good. (I'd post examples, but it hasn't happened yet and I don't want to inadvertantly invite everyone on TeX.SX).
For fun, here's a simple postcard: