Intern!!! Especially in marketing and advertising! I swear those industries are run on the backs of free labor
Does your college have a career center? Also, you could also go to your department's office or website and they will be chock full of information regarding internships. I did internships in promotions (concerts, radio, etc...) with Clear Channel and did one that related to marketing, events and public outreach with the Grammys in Nashville (best experience of my life). They were both unpaid, but for college credit. You will be lucky to find one that is paid, but they are out there. All of my internships (I've had 4) were through my school (that's a stipulation and how they get away with not paying you
), so that would be the best place to start.
ETA: I didn't find my internships through the career center at my school, but I did have to go through them once I obtained it. I researched where I wanted to intern and what I wanted to do and then applied with the companies I wanted to work for. The career center only assisted with the paperwork after the fact.