Copperheads, Cottonmouth aka Water Moccasin, which really count as one, Western Diamondback Rattler, Timber Rattler, Western Pygmy Rattler, and Texas Coral Snake, so really six in all.
There is also a multitude of non-venomous species, some which closely mimic the venomous ones in coloring and pattern. Almost impossible to tell the difference unless you get very close up and personal and have the where with all to determine if they have triangle shaped or rounded heads, round pupils or slits, viper holes above the nose holes in the head, etc...and in the case of Coral snakes, can remember the old adage: Red touches yellow, kills a fellow!
The color pattern on a coral snake is a red touching yellow pattern with black between the red touching yellow band. On snakes that mimic Corals there is a black band separating the red and yellow bands.
Coral Snake Milk Snake
From this example you can see what I mean by getting close up and personal to tell the difference.