This site offers literally hundreds of fantastic flashcards that can be used to teach any language. Useful for low levels, ESL/ESOL and mixed nationality situations. The cards are clear, arranged in sets and can be searched by tags. They are with an American English learner in mind but can be used to teach any language. They can be printed off as words or images to a PDF file in a variety of sizes. A great teacher tool and resource which saves time in preparation.
You can print them out in different sizes as well.