I'd advise against it. When mixing species in any set-up one of the keys to long term success is to have species that will occupy different areas of the terrarium. i.e. mixing terrestrial and arboreal species or nocturnal and diurnal species. Ideally you have one species that is diurnal and one that is nocturnal, and one that is terrestrial and one that is arboreal. Mixing phelsuma geckos with tribilinotus skinks or fattail geckos could work well. The phelsumas would hang out in the top of the viv and be active during the day while the Fattails or Tribs would stay on the ground and only really come out after dark. That way there is no competition for feeding or sleeping areas and there is no chance of random exploring by one species upsetting the other one while they're sleeping.
Mixing Banded and Leopard Geckos would most likely end in tears. The animals would be competing with each other on every level. For food, for sleeping spaces, for heat, everything. The larger one(s) would most likely end up dominating the smaller ones leading to a failure to thrive, possibly resulting in the death of one or more animals. Doesn't sound like much fun to me. If you wanted to do an arid, mixed species vivarium I'd advise selecting either Leos or Bandeds and couple them with a similarly sized arboreal gecko from northern africa, or the australian interior. Tarantolas could be a good choice, maybe even Phelsuma Standingi as they tend to like things hotter and drier than other phelsumas and perhaps an Oedura or two.
The other important things to remember for any mixed species set-up is to allow more space than either group would need normally, and to select species with similar environmental specifications. Making sure your animals have lots of space to avoid each other goes a looooooong way towards maintaining the long term health of your animals. Crowding together animals of the same species can put a lot of stress on them, when you toss in different species and crowded conditions you have a recipe for disaster. The second point seems to me a no-brainer. Don't put Cat Geckos which can die in temperatures much above 80 and like lots of humidity with Lygodactylus who come from hot, dry forests in Africa!
Keep these considerations in mind, and always take the time to plan out your viv before you start buying animals and you can have yourself a lot of fun. Best of luck to you, hope this helps.