A Milli with R. cili

Crested Geckos Rhacodactylus ciliatus
Millipedes (eg. African Giant Millipedes Archispirostreptus gigas)

Although I personally never tried this combination there are many people who house the two together without any problems and while these large millipedes may seem unsettling to some, they are very beneficial to those who are keeping naturalistic terrariums.

Millipedes are beneficial to the vivarium because they eat left 

over crested gecko food aswell as any decaying plant matter.

For this combination I recommend at least 20 gallon tall tank which will safely house both species . The general rule that you want to follow is that the cage is twice the length of the millipede, as deep as the millipede is long. While floor space is more important than height for the millipedes it is still important to have a tall enclosure with climbing opportunities for the crested gecko. Make sure the enclosure has a secure lid. Millipedes and crested geckos, like to eat soft fruits (I use baby food). These guys will also eat the Powdered Crested Gecko Diet if it is available to them. You also want to make sure that you have a shallow water dish with clean water available at all times.

Crested Geckos will do very well with Millipedes, and the Millipedes will quite readily breed when a male and a female are housed together, so you could very likely end up with babies if keeping the opposite sex together. The temperature during the day needs to be at least 72 degrees F. They also like to burrow, so a three to four inch layer of peat moss, or peat moss mixture is recommended for their substrate. Millipedes secrete an irritating liquid in self defense, usually when handled by owners. I shouldn’t have to say this but be sure to wash your hands after handling millipedes as their secretions can cause major irritation or death.

It is also important that you do not directly spray your millipedes with water because they breathe through their skin and they have symbiotic body mites. These mites clear any obstructions blocking their hosts spiracles (breathing holes).. Although they are mites, they will not affect the crested gecko (or any other animals). Directly spraying a millipede with water could wash them off. These "mites" play an important role in the millipedes health, trying to rid a Millipede of them could result in death.

These species make a great combination. Though I never had one, they do not seem to show any sort of aggression towards one another and can live together quite peacefully.