KMK, this is actually a subject that has become a topic of interest in our household. We never expected to reach that point, but now it's looking as if we need to address the issue in the next couple years. I don't have any answers for you, but want you to know that I'm interested in the answer, too. I'll probably start planning a blog entry on the subject, though it may take a while (as in weeks or months) for it to actually find its way to publication.
My understanding is that if you contribute to a Roth and then aren't eligible at the end of the year, you can get out of it without any sort of penalty. You'd just have to pay taxes on your capital gains. Don't quote me on that, but that's what I believe is true. As for other options: as far as I know, a traditional IRA doesn't have any sort of earnings cap. You're taxed at the back end, but I think you get a tax deduction when you put money in.
Hopefully Dylan will come along and answer the question for both of us.