If you didn't know, I'm a complete geek about words and language usage. Idioms have always been a fun area of exploration for me. I even read books on idioms from around the world (still need to add those books to my permanent library!).
Last night, when I accidently stumbled on an online dictionary of idioms, I actually squealed out loud in delight.
It's very good for explaining what the idioms mean. However, it falls short by failing to mention origins. I have a strong desire to learn *about* them beyond just what they mean.
Go there type in a word and see what idioms come up. "Rose" was the first word I chose.
http://idioms.thefreedictionary.com/