I would REALLY like to see spell check added to the WP feature list, though I understand it might be hard to implement. I like the thing where you can highlight a word, click "dict" and have dictionary.com do a lookup, but it's not enough. As it stands once I write my entry I copy it into Microsoft Word (or the Open Office word processor), do a spell check, and then copy it back into Word Press. I did this back when I was using Moveable Type too.
When w.bloggar 4.0 is released it's supposed to have WordPress support. This would solve my problem because it has spell check built in, but I still would like WordPress to natively support it when I'm away from my computers.