iPhone Apps for Studying Japanese

I thought I'd start this topic to help with those of us that have an iPhone. Could anyone that has one and uses it to study Japanese list here which apps they use specifically to study Japanese? It might be helpful to the rest of us - particularly regarding paying apps and perhaps reviewing them before anyone shells out for them (because many apps don't seem to have reviews on them, and I'm not willing to test the waters all the time).

I've added a review of the ones I've got further down, as I couldn't add the review to this post for some odd reason. Read on....