Sequential Spelling has been great for us. I have an awful speller, and a natural speller, and it works well for both. It's very pick up and go, no prep time required. The lists are based on patterns in spelling, for example, all, tall, stall, install, installment. There are no lists to memorize, but the student takes a test every day, and patterns are repeated throughout the week, and revisited. This really helps my bad speller to have to think about the words and learn them, not just memorize a list for a week, spit it out, and then forget it the next week he has to write something (which is what happened before).
My two cents, hope it helps!