OP: What geographic are you in? Major? What field do you want to work in? Give us some more details.
Take advantage of your school's on campus recruiting. My only regret from undergrad (other than graduating on time) was not informing myself of the timeframes and getting in on some of the better employers. Second, let that same office review your resume and cover letters.
After that, I've always used Dice and Craigslist. I have my resume confidentially searchable on Dice (basically they can get my skills inventory and years of experience, but not my name, they contact me through the Dice system if they want). Be sure to not use stock cover letters, force yourself to write a specific one for each job you're applying, and have multiple resumes too, each tailored towards different positions and emphasizing different skills and attributes.