Where should the letter live?

You can host it on your own site and embed a form to collect signatures. Alternatively, you can use a petition site, like change.org or www.thepetitionsite.com to host your letter. If you’re interested in making a free page on www.studentsagainstsurveillance.com, email April for more information. Also, consider limiting the signatories to email addresses from your college or university (.edu).

On May 7, the Electronic Frontier Foundation published an electronic call to arms: "Join Students and Scholars In Speaking Out About the Effects of Mass Surveillance on Campus". It mentions an initiative I've been involved with over the last few weeks: after a meeting between the EFF and the Student Net Alliance, I was one of three NYU students (the others being Luc Lewitanski and Hannah Weverka) who wrote an open letter protesting dragnet surveillance, talking about how it negatively impacts students as a subset of the population.
Backed by the EFF and the SNA, we published the letter on studentsagainstsurveillance.com/ and allowed students and faculty to add their name to the letter. So far, almost a hundred student and faculty members have signed on, and the local NYU paper covered it. 

As we gathered more signatures, April Glaser, our contact at the EFF, mentioned a planned initiative to get other universities to write protest letters. I pitched the idea that our domain, studentsagainstsurveillance.com would host these protest letters on subdomains. If the idea took off, we'd become studentsagainstsurveillance.com/nyu, Columbia, for example, would be .com/columbia, or the University of California, Santa Barbara would be .com/ucsb. The EFF liked the idea and we're now waiting for more universities to write letters. 
In terms of continuing the work the letter starts, I'm working on two projects: a short template other universities could use [1] and some sort of site which logs local aberrations. I think our letter benefitted from the mention that the NYPD was monitoring Muslim student organizations at NYU and Columbia: students sort of knew the NSA was spying on everyone, but it was news to 99% of the NYU students I spoke to that the NYPD had been monitoring their campus. [2] For a lot of people, this seemed to bring NSA spying into their own backyard, out of the realm of disconnected DC politics and into their everyday lives. I'm weighing up how much work would be involved in doing a state-by-state list of concrete ways the NSA dragnet is being used against college campuses. To borrow the words of David Foster Wallace, who was speaking about political disillusionment among young American voters, the trick is to get people to "try and stay awake". 
Another very nascent idea I'm considering is hosting a PGP/OTR how-to event, specifically targeting journalism students. Most of the journalism students I've spoken to are reasonably tech-savvy, but haven't given much thought to how the EFF dragnet will affect their ability to work with sources. Snowden has said that "Encryption works. Properly implemented strong crypto systems are one of the few things that you can rely on." [3] Even though PGP in particular is still pretty hard for non-technical students to work with [4], I think it's important to teach students how to use PGP despite that complexity.
As I work more and more with other advocates of digital rights, the worries I mentioned in "Speaking Up: preliminary thoughts on advocacy and the internet" (that I'm being a stereotypical college pseudo-activist) dissipate. The letter's something concrete that's started some discussion on campus, and it's part of a wider campaign organizations like the Student Net Alliance are mounting. The work waits.
Interested in getting involved? You can e-mail me (tommy@collison.ie) April at the EFF (april@eff.org). 
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[1] Although the EFF deeplinks post does a good job of starting you off.[2] http://hosted.ap.org/specials/interactives/documents/nypd-msa-report.pdf
[3] http://www.theguardian.com/world/2013/jun/17/edward-snowden-nsa-files-whistleblower?CMP=twt_gu
[4] Hat-tip to Keybase.io for trying to solve this problem.