YouGlish - great resource for focusing on a specific sound or word (be sure to click the US button to filter out British and Australian accents, speed can be slowed down to help the student process difficult sounds)
Visual and Audio Resources
Mouth positions - These pictures of mouths making specific sounds may help with mouth positioning and pronunciation
Pink Trombone - Fun game to show how various parts of the mouth influence pronunciation (build a vowel, and then play with consonants; easy ones to start with are "bee" and "me")