As a computer science student at Michigan State University, I have been told repeatedly that one of the best things I can do for my career at this point is take on an internship for a semester (usually summer). I have already done one internship (at NASA ARC) and am hoping to do another one this summer with a well known company.
I have sent applications with my resume and such to Google, Microsoft, Zynga, and IBM. I was impressed with the ease of the process — all four employers made the application process quite efficient.
Of course, I could always just work full time at my current job at the National Superconducting Cyclotron Laboratory over the summer. That is my default plan. However, if I get an offer for a nice internship, I probably would not turn it down. It is always nice to get away from campus for a bit and learn some new skills.