Odyssey is the best replacement battery as far as I know. However, it's right up there with the Optima in terms of price.
Since there are only 6 or so major battery manufacturing plants in the world, you can be assured that most batteries all come from the same place, they just slap different logos on them. Personally, if I wanted something a bit cheaper, I'd probably go get a Sears DieHard battery as they've always been good to me.