This is the jack-pot of all websites. You'll get a quick snapshot of why idioms are important but the real treasure is all the resources linked on this site. Websites, worksheets, books, and apps are all listed here.
These task cards are a great addition to a literacy station or to be used as a whole class activity. Print them out, for free, and use them again and again. I especially like having students work together to figure out what the idiom means.
The thing I like most about this site is the sample dialogue provided. The examples are quick and easy with content that is student friendly. You can also check out the tips to teaching idioms on this site.
If you aren't sure how to begin incorporating lesson on idioms into your curriculum take a look at this site. This shows a three session lesson with objectives and standards included. I find it helpful to take a look at what other teachers are using and modify it to fit the needs of my students.