Designed for 1st-2nd grade students, Murky Reef combines reading and math skills in the context of exploring a coral reef. This is the free version, though there is a more robust version available for $3.99. Students can review numbers, sight words, and vocabulary. There is some reporting built in.
This app has been featured in the Apple iPad commercials for teaching young students to write their letters. Beyond the ability to trace, the app also records letter sounds, names, and phonograms.
Common Sense offers great reviews and advice to parents as well as educators. Their new Beta site - Learning with Technology - reviews apps, games, and other media for kids in terms of learning.
"Lexico-Cognition is an App to develop language understanding, vocabulary building, cognitive, memory and auditory skills in a playful way. It was developed and tested by qualified speech therapists. "