>>My girlfriend wants to get a fairly large reptarium for a crested gecko, but she's interested in purchasing a different species to live with it. What other species live in simlar climates and wouldn't attack the crested? I suggested a gargoyle gecko.

Some people have interbred cresteds with chahoua, so presumably they could coexist in a tank. Usual disincentives apply, generally recommended to keep animals separately, you have been warned, blah blah blah...
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0.1 Albino Leopard Gecko - Tigger
0.1 Crested Gecko - Pooh-Bear