Your mission, should you decide to accept it, is to put a poster into the tube, travel to the conference location, and present the poster. And if you've already applied to present a poster and gotten accepted, then it kind of behooves you to do that. It's not a great idea to pull out of a conference after being accepted.
What conference do you want to go to? Generally, your advisor, other faculty, or random people will forward you links to conferences you may wish to consider attending. You may also want to search out conferences on your own, but to preserve the signal to noise ratio, I suggest that you look at where others in your field have already presented, and consider attending there. Google is not the answer here.
I would be willing to go back to VSS, because it was a very comprehensive conference that covered all aspects of vision. I feel that if I do good work in that area, there will probably be a place for me, and content that I will find interesting.
Looking at some of the other labs that I admire, including the Computational Visual Cognition lab at MIT, and Helene Intraub's lab at University of Delaware, I see that Helene Intraub often presents at VSS, and occasionally at the Psychonomics Society conference . The Computational Visual Cognition lab often presents at the Cognitive Sciences Society. The Cognitive Sciences Society conference in particular seems like an interesting conference for Information Science Students, as it states that it is an interdisciplinary conference. This is not unexpected, given the interdisciplinary facets of cognitive science.
Other conferences I am currently thinking about submitting proposals to include ISCRAM 2009, The 6th International Conference on Information Systems for Crisis Response and Management, which has a section for HCI related issues.