My brother houses a golden gecko with a crested, and doesn't seem to have any problems. Golden geckos require *slightly* higher temps than cresteds, but he's got a tall enclosure with a lamp on top, so basically what happens is the golden spends a bunch of time in the upper areas of the enclosure, and the crested stays lower most of the time. They don't really get in each others' way much. Goldens are not ideal pets, however; they tend to be skittish, not liking to be handled, and they are *FAST*. My brother has tons of experience handling them, and reptiles in general, and he still avoids handling that gecko any more than he has to, and occasionally loses control of it when he does handle it.
At least one person on the boards here has a big millipede in with one of his cresteds, and that's supposedly ok. Whatever you do, everybody in the tank needs to be of similar size and habitat requirements in order to even have a chance at living harmoniously, and you'll have to watch things pretty closely at first, in order to ensure that no fights or predation attempts are occurring.
Since you already know that it may or may not work well, I won't harp on that point except to recommend that you be extremely careful, and that you wait to set this tank up until you have a lot of free time to observe the goings on. Make sure that you have a separate tank available for housing some of the animals in case of incompatibilities/bullying/dominance issues.
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0.1 Albino Leopard Gecko - Tigger
0.1 Crested Gecko - Pooh-Bear