Eh. Snakes are all pretty stupid. As Neal stated, many colubrids are very inquisitive and visual....which makes them seem more intelligent. Again, being a colubrid doesn't qualify for special status - colubridae is nothing but a taxonomic dumping ground for snakes that haven't been properly classified.
If we are discussing qualities that mimic perceived intelligence; well then there are several species that combine inquisitiveness, general activity and an alert demeanor which make them seem like the mensas of the snake world when compared to lumps like ball pythons and boas.
Psammophilines (psammophis, psammophylax, rhamphiophis) are all very curious and active snakes - as well as visually stimulated. Same goes for the dispholidines (thrasops, rhamnophis, dispholidus, thelatornis).
Drymarchon are often claimed to be intelligent, but I have a few that are pretty dumb and ball-pythony. I also have a few that have acclimated well, are fairly interactive and seem interested in what's going it.
Hydrodynastes are also a species I would put in that class. Clelia are endearingly goofy, and most philodryas species are indiscriminate biting machines.
If you are interested in an intelligent reptile buy a tortoise of a heloderma. Our russian tortoise is like a dog and our heloderma each have individual personalities and are extremely interactive.