The movie posters out of your dorm room just aren't performing anymore. Find a home furnishing store you like and go nuts. Picture frames, canvas art, decorative lamps, vases, sculptures, and throw pillows. I'd personally recommend Bed, Bath, and Beyond or Indigo. They always have stylish, affordable home decor you'll love. Help your house be a reflection of yourself and you will be surprised how much happier you feel there.
Every chapter of your life has a lot to offer and it would be unfortunate to waste whenever at all. Your 20's are such a special time in your lifetime that is often ruined by expectations, judgements, and just plain being overwhelmed. Don't allow that to take place, enjoy every little thing this decade in your life provides.