Melissa asked for a link to the handheld electronic spelling dictionary I mentioned in my writing post. We have a Franklin-Merriam Webster handheld dictionary that's sort of like this, but not exactly. (It's a little older, I think.) I picked it up at Border's because I saw it and I had been thinking about getting something of the kind for a long while. Since I have a tendency to forget things I wanted to do and remember them later only to forget again, I went ahead and bought it. But...
It looks like there are also cheap, electronic spelling correctors on the market, too. $13. Not too bad.
I have found a spelling book for my older kids which I am hopeful about, although we haven't started it yet. I ran across a mention of it on the 4real forums (but unfortunately I can't remember the exact thread). The name of the book is Spell of Words -- which is kind of a goofy title, but since it was written for older dyslexics, it lays out the essential spelling rules in a logical, succint manner. This is exactly the format I've been looking for in order to do some remedial work. But... we'll see how it works out in practice.
(A note about the links: I've mostly given up the Amazon Associates program. I've made $20 in 4 years. So these links won't net me any money. If you buy a book from the sidebar, however, I might get a kickback.)