This SMART Board sorting activity is a wonderful way to introduce/practice vowel sounds. Students sort between pictures that have the appropriate sound (and placement) and pictures that do not. There are 4 pages for each vowel (initial short vowel, medial short vowel, initial long vowel, and medial long vowel). The 4 "A" pages are pictured.
This correlates well with the ImagineIt Language Arts Kindergarten curriculum. This curriculum always introduces initial vowel sounds on the first day, and medial vowel sounds on the second day (for short vowels first, and long vowels near the end of the year).
I use this activity throughout the school year as a supplement to our district's curriculum language activities.