What are some good mermaid legends/myths ?
I agree with Shabenrocks, the original legend of the Little Mermaid is really good, it was one of my favorites growing up though its really sad at the end and not a lot of people know about it anymore.
the little mermaid
Sirens are similar to mermaids
Grimm's fairy tales might have some, but if you look in some greek mythology books, your bound to find some.