Lists of vowel digraphs are available at EnglishHints.com, About.com and BogglesWorldESL.com. All three sites include common words that use each digraph, and printable activity sheets are offered at BogglesWorldESL.com.
A vowel digraph refers to a single phonetic sound in the English language that is created by two vowels. Unlike a diphthong, a digraph is a unique sound that does not contain the sounds of either vowel. Some vowel digraphs produce a long vowel sound, such as the long "e" sound in leaf or the long "a" sound in rain, while others create a distinct sound such as the "oy" digraph in boy or the "oo" combination found in moon.