I don't really believe in "beginners." However I do know that a lot of people will suggest Leopard Geckos, African Fat-Tails and Crested Geckos. Pictus (Paroedura picta)and Dwarf Sand geckos (Stenodactylus sp.) are also nice to keep in a gecko colony, provided they have ability to set up their own territory between them. Well... not gecko colony, but really there is enough space in that 55 gallon for them to stay clear without feeling stressed and harming the others.
There are lot you can keep in that 55 gallon of yours. There are some you can keep, others you cannot. Everything is about footprint. For instance, Bearded Dragons would be better in a 40 Gallon Breeder or 50 Gallon as they are 19" in width, rather than 13"