A Cowl-Neck Sweater
A Crew-Neck Sweater
Mock Turtle-Neck Sweater: a popular style, classic and beautiful. The neckline is narrow enough to lie flat against the neck, while still maintaining a comfortable fit.
Shawl Collar Pull-Over Sweater: has a distinctive cross-over style of neckline. This neckline is luxuriously warm, and very distinctive when worn
Shirt Collar Sweater: most often emmulated with a button-up shirt under a crew-neck sweater with the collar open and laying on top.
Stand Up Collar Sweater: also called the "Jackie Kennedy collar", is a modified version of a mock turtleneck neckline. It is higher, wider and more shallow than a mock turtleneck, and instead of hugging the neck the way a mock turtleneck will do, it stands up and away from the neck. This is a very fashionable design feature.
Turtle Neck Sweater
Standard V-Neck Sweater
I'm sure I missed something. I'll update as I find more sweater/collar types. Feel free to post more varieties I haven't mentioned in the comment section below. Thank you for your time, and stay beautiful (and warm this fall)! xoxox