Largest and Smallest

Largest:
Crocodile: Saltwater Crocodile, 13-18 feet long and 1300- 2000 lbs. (Largest ever was 20 feet long and 2900 lbs!)
Lizard: Komodo Dragon, 6.5-10 feet long, 150 lbs
Snake: Most Massive:Green Anaconda, 23 feet long, 550 lbs
Longest: Reticulated python, 28 feet long
Largest Venomous (overall): South American Bushmaster, 12 feet long, 19 lbs.
Longest Venomous: King Cobra, 18.5 feet long
Heaviest Venomous: Eastern Diamondback rattlesnake: 26 lbs
Turtle: Leatherback Sea Turtle: 9 feet long, 2000 lbs
Tuatara: Brother's Island Tuatara: 30 inches long, 3lbs

Largest Reptile ever: (based on one vertebra) Amphicoelias: 60 meters long, 122 metric tons! (Link shows in comparison to 6 foot human)

Smallest:
Crocodile: Cuvier's Dwarf Caiman: 5 feet long
Lizard: Jaragua Sphaero, 16- 18 millimeters (Can curl up and fit on a dime!)
Snake: Barbados Threadsnake, 10 centimeters long
Turtle: Speckled Padloper Tortoise, 2-3 inches long, less than 100 grams (the weight of a medium sized tomato)