Depends how chilled you want to seem and what mood you're in, as chillin' takes many forms and doesn't always mean slow and relaxed music. Some people chill to bob marley some to classical music. For a middle of the road selection may I reccomend the following:-
Norah Jones,
Marvin Gaye
Joss Stone
Corrine Bailey Rae
Jack Johnson
if you want something diffrent try a group calld hiroshima there from LA very chilled out group. There the type of group you can have on at 4 in the mornng after a good nite out just to kick back and chill to