Two player card games?

As you might imagine, we're spending a fair amount of time sitting around either waiting for transport or travelling. There's also the inevitable nights when it's raining or cold and we want to sit in a cafe and chill out. Ploughing through English language books is one option, but finding enough books to keep the engine running is expensive and difficult.

So anyone got any tips for good two player card games? I bought Holly a book of card games for her birthday, but most require either more than one deck of cards or more players. We've almost played out Rummy...