You know if the App Store has been out for a month and we're posting about a web app, it has to be a good one. Google announced late last week that they've brought the terrific Google Translate service over to the iPhone. Of course, whenever you travel internationally, roaming charges (sometimes huge ones) can come into play, but if you find yourself tooling around Spain and need more phrases than ¿Dónde está el baño? or Tú eres mi chica, Google's web app will do the trick fast and easy.
And there's some nice coding in there, too -- the phrases translated get stored on the client side of the phone, so if you've already translated something, you don't have to reload the page to see it again. To use the service, just point your MobileSafari to translate.google.com. Folks in other countries probably still won't care too much what you have to say, but at least they'll know what you're saying.