Spring is conference season for many major professional associations including the American Planning Association. However, if you missed APA this year, or even if you didn't, a number of more specialized groups meet over the summer in smaller and more focused settings. Student registrations and deals on accommodation can make these very affordable.
The one I am attending this year is the Planners Network in Memphis, May 18-21: http://www.memphis.edu/plannersnetwork/. The cost at this stage-for both students and others--is $335 for the conference, all meals, and lodging shared by two people (they'll match you if you need). It is a little more to stay on your own. You just need to get to Memphis! Planners Network conferences are known for their participatory workshops with local communities and interesting cultural receptions reflecting the organization's interest in social equity and environmental justice.
The Congress for the New Urbanism meets in Wisconsin on June 1-4: http://www.cnu.org/cnu19/. These conferences have grown quite large. I've only been to one and was struck by how much of the conference was a dating game matching consultants, local governments, and developers. However, that is interesting in itself and there is typically some vivid debate between larger than life characters. The student price for 4 days of registration is $125 (going up on May 6); the registration rate for non-student, non-members is $585.
I'm sure there are other summer conferences of interest but these two represent some of the range of summer opportunities for meeting others who want to make a difference.