You could try some Sceloporus or related lizards
That cage would be big enough for several. I'd reccomend finding a colony (I've always seen them in groups in the wild) of a local species, and try to replicate it's conditions. Most of the time either good rockpiles, or dead trees, will have colonies of these lizards on/in them. Depends on your part of the country.
Also you could do whiptails/racerunners. Depends on where you are, as some species are protected in some locals
. But for small, observable lizards, lots of North American species are great. I don't and haven't kept them myself, but I know of several local colonies and frequently go to watch them for a while when I can. There's one of some Holbrooki species on a large dead cottonwood nearby that's absolutly fascinating to watch.
So I'd just find some local Scelops, Holbrooki, whiptails, etc. that appeal to you. Read up a bit on their care to get diet info and whatnot, and replicate thier natural surrondings. Dead tree with large cracks in it (they'll use it for shelter), rock piles, shrub brush, etc. 75 gallons gives you room to play with. These lizards are typically small; I think the largest N. American scelop is under a foot. Most are about 6-8 inches. You could likely keep 3-5 in that cage (they're active). Whiptails tend to be larger, but there is a range; the checkerd gets huge (15"
whereas some N. American species stay under a foot total length. Probably about the same number would work.
The scelops et al tend to be more tree/shrub dwelling,a lthough some species will be found in rockpiles. Whiptails tend, in my area, to be found more on rockpiles like we've got in the canyon.
me