Depends where you live. The prairie areas of the west and SW sides are great for Kings (Speckled and Prairie) and TX Rats. The piney woods of the north side of town are good for LA Milk Snakes (in the right habitat), Copperheads, etc. The southeastern side of town has water snakes, kings, mud snakes (although they are everywhere, just hard to find), etc. Eastern Hognose used to be really common along Buffalo Bayou on the west side of town in the sandy soil along the bayou.
Find some trash piles. March and April are the premiere months.