“Cool Spanish” (BBC Languages)
The BBC Languages web site has a section on slang expressions in Spanish:
http://www.bbc.co.uk/languages/spanish/cool/
This is divided into 16 thematic sections on topics such as Food, Friends, Money, Swearwords, etc.
You can listen on the site to the phrases one at a time and read an accompanying explanation. You can also download the phrases in each section as an MP3 file.

