What's your budget?
Our kids were asking for ipods, but the cheapest non-shuffle ipod is more than we're willing to spend, and none of us like the whole shuffle concept. It was telling, though, to compare the kids--it's was very clear that with our daughter (6th grade) it's a fashion/status issue, while with our son (2nd grade) it's a listening to music he wants to listen to issue.
We're getting the kids
these, but then again our main criterion was "cheap enough so we won't scream
too loudly if they lose it/step on it/decide to trade it to their 'best friend' for a pack of chewing gum." (I hope this isn't a consideration for Mr. Rat.

)
A lot of the models have changed, but I think you still have to do some thinking on the flash vs. hard disk issue--it's almost pointless to compare between the two categories.
Oh, and I came awfully damned close to getting
these. I may still order one just to see how they are. (Yes, I know there's no memory, but 1GB SD cards are going for a song these days.)