Other ancient reptiles

Marine Reptiles:

Ichthyosaurus: Dolphin-like body shape, large eyes, powerful tail flukes.

Plesiosaurus: Long neck, small head, four paddle-like flippers.

Liopleurodon: Massive size, large, broad skull, powerful jaws.

Mosasaurus: Large, lizard-like body, powerful jaws, strong tail fin.

Nothosaurus: Long neck, flattened skull, webbed feet (transitional form).

Tanystropheus: Extremely long neck (several times the length of its torso).

Placodus: Blunt teeth for crushing shellfish, bony armor on its back. All the placodonts look like kind of like turtles, some with two shells (one in front and one in back) like Psephoderma or Cyamodus. Henodus's shell was almost square and pretty flat. It's just convergent evolution, though: their shell is modified skin, not modified ribs.

Elasmosaurus: Exceptionally long neck.

Pliosaurus: Short, powerful neck, massive head with conical teeth

Atopodentatus: Marine reptile with a "zipper-like" toothed upper jaw split down the middle.

Dinocephalosaurus: Aquatic protorosaur with an extremely long neck, making up more than half its body length.

Hypuronector: Elongated body and large eyes. Large, paddle-shaped hands and feet. 

Eretmorhipis: Tiny head and especially tiny eyes, oversize flippers, a duckbill and spinal plates.

Pterosaurs:

Pterodactylus: Relatively small, long beak, no bony crest.

Pteranodon: Large pterosaur, prominent backward-pointing crest.

Nyctosaurus: Distinctive, long, antler-like crest on its head.

Rhamphorhynchus: Long tail with a diamond-shaped vane, forward-pointing teeth.

Tapejara: Prominent, often elaborate crest on its snout and head.

Quetzalcoatlus: Enormous wingspan.

Dimorphodon: Large, robust head, relatively short wings.

Dsungaripterus weii: Upward-curving lower jaw and a prominent head crest starting midway along its snout.

Pterodaustro: Long, upward-curved lower jaw filled with hundreds of bristle-like teeth for filter-feeding.

Crocs: Crocodylomorphs are archosaurs, as are dinosaurs, unlike anything else on this list. Modern crocs are descended from them,

Sarcosuchus: Enormous size, bulbous growth at the tip of its snout (bulla).

Stomatosuchus: Long-snouted crocodylian, needle-like teeth.

Kaprosuchus: Heavily armored snout, large, forward-projecting canine-like teeth ("Boar Crocodile").

Simosuchus: Short, blunt snout, leaf-shaped teeth ("Pug-nosed Crocodile").

Anatosuchus: Flattened, duck-like snout.

Champsosaurus: Resembled a gavial, extremely long, slender snout.

Dakosaurus: Short, broad snout, large, serrated teeth.

Suchomimus: Long, slender snout, sail on its back.

Thalattosuchus: Marine crocodylomorph with paddle-like limbs and a hypocercal tail fluke like an ichthyosaur.

Arizonasaurus: Impressive sailback, like a croc version of Dimetrodon or Spinosaurus.

Etjosuchus: Bipedal, with small front limbs, with a skull over two feet long. Basically the croc version of a T-Rex.

Proterosuchus: Long snout with a downturned tip (crocodile-like appearance).

Erythrosuchus: Large, predatory archosauriforms with disproportionately large, massive heads.

Estemmenosuchus: Large, herbivorous therapsid with multiple horn-like structures on its skull.

Hupehsuchus: Enigmatic marine reptile with a long, narrow, toothless snout, split dorsal plates, and extensive body armor.

Other Prehistoric Reptiles:

Dimetrodon: Large "sail" on its back (elongated neural spines). (Not a reptile)

Edaphosaurus: Similar to Dimetrodon but with crossbars on the spines of its sail. These two are closer to mammals than they are to reptiles, I just included them here because laymen think of Dimetrodon as a dinosaur.

Scutosaurus: Bony scutes covering its body.

Pareiasaurus: Bony knobs and ridges on its skull and body.

Captorhinus: Multiple rows of teeth in its jaws.

Coelurosauravus: Archosauromorph with elongated ribs forming a gliding apparatus, similar to a flying squirrel.

Cotylorhynchus: Large synapsid with a disproportionately tiny head and a massive, barrel-shaped body

Drepanosaurus: Arboreal reptiles with chameleon-like eyes, bird-like heads, grasping hands and feet, a claw at the end of their prehensile tail, and a hump on their back.

Longisquama: Small reptile with extremely long, ribbon-like scales (or feathers) projecting from its back.

Odontochelys: Early turtle with a fully developed plastron, a partial carapace, and teeth.

Vancleavea: Medium-sized archosauriform characterized by its unique arrangement of osteoderms and elongated body.

Eunotosaurus: A parareptile with broad, flat ribs that were believed to be an early step towards the development of the turtle shell, although not directly related to turtles. 

Drepanosaurus: A reptile with a very short, triangular-shaped skull, a chameleon-like grasp, and an exceptionally long, curved claw at the end of its tail. 

Sharovipteryx: A bizarre gliding reptile with a membrane of skin between its legs, rather than its arms. It had long, slender legs and a tail, with its wings located between its hindlimbs and its tail. 

Cotylorhynchus: Pelycosaurs with extremely robust bodies, small heads, barrel-shaped rib cages, and powerful limbs with thick bones.

Sclerocephalus: A large, amphibian-like temnospondyl with a very broad, flat head, a short snout, and many teeth, including fang-like teeth on the roof of its mouth. 

Trilophosaurus: A reptile with a surprisingly short and blunt snout, often likened to a bird's beak, with powerful teeth adapted for crushing plant material. 

Shringasaurus: An early take on making something to fill the niche of a sauropod. It had a horned head, legs and feet that kind of resemble a crocodile, and a barrel-shaped body.