Still looking for a summer internship? The 2012 Google Summer of Code (GSoC) starts accepting application from students on Monday March 26.
GSoC is a global program funded by Google that pays undergraduate or graduate students a $5000 stipend to write code for open source projects. GSoC has worked with the open source community to identify and fund exciting projects for the upcoming summer. Last year over 1,100 students were funded by the program. The FAQ is a good place to find out more.
A set of open source projects (aka mentoring organizations) has been selected. Students apply to work on one of more of these and each mentoring organization ranks the students interested in working with them. Google facilitates the final selection and pairing. The mentoring organization works closely with the student to define tasks, check progress, help solve problems, etc. Typically the student works remotely, interacting with his or her mentor via email, chat, skype, etc.
Students can submit applications via the Google Summer of Code 2012 site from March 26 to April 6. Google says that that the best applications they receive are from students who took the time to interact with one of the participating mentoring organizations and discuss their ideas before submitting an application. So your first step should be to look at the list of 2012 GSoC Mentoring Organizations and contact some that have projects that interest you and for which you have the right skills and background.
See the GSoC 2012 Program Timeline for a complete schedule. You might also check out the information on the Advice for GSoC Students Page and the GSoC forum.