Get a babysitting job. Look on bulletin boards in apartment buildings, stores and community centers for babysitter want ads.
Tutor students who need extra help. Determine your strongest academic subjects. Post fliers around campus and in local elementary schools and high schools describing your skills and your availability to tutor. Send out emails to friends offering your expertise.
Find a work-study position in your college. Go to your school's career center and speak with a career counselor. Getting a job at your school is easier than getting a job in a local store or restaurant because there is less competition and your school has special jobs set aside for its students.
Sell your old textbooks. Put up listings on auction sites. Some college bookstores will buy used textbooks.
Donate plasma. You can have your blood drawn about once a month. Every time you donate, you make about $35-45.
Participate in your college's psychology studies. If your school has a good psych department, there will be many undergraduate and graduate students who need subjects for their experiments.
Take good class notes and sell them. Many students don't take great notes or they ditch class. Either way, good class notes are often in demand, especially before exams.