EnchantedLearning.com and SpellZone.com both offer a list of words that contain the long "e" sound. SightWordsGame.com has a similar of 275 words that contain the long "e" sound, categorized by spelling.
A shorter list with pronunciation tips appears on Pronunciation.com. 123TeachWithMe.com has lists of words with either short or long "e" sounds for a comparison of the two pronunciations.
In English, it is important to pronounce the distinction between the short and the long "e," as it can change the meaning of the word. For example, "bread," pronounced with a short "e," and "breed," pronounced with a long "e," have very different meanings. In the spelling system, the long "e" has multiple possible spellings, including just "e" in "he," "ea" in "heat," and "y" in "angry."