A stampede of users leaving the likes of Google, Facebook, etc. would put pressure on those companies to use their resources to fight it 'at home'.
I realise this is a relatively naïve POV, but you only have to see how quickly Instagram reversed their ToCs a few months back - after users started closing their accounts in droves - to see how this can prompt the big boys into action.
You could also argue that there's a real opportunity for a European competitor to launch a rival to these services, under the guise of our strong data protection laws (in the UK at least). So if a DropBox or Gmail clone (for example) started to get traction, again it would put pressure on.
The only thing companies like Google and Facebook can do to improve matters is to stop collecting and storing giant troves of personal data.
I'm not sure it's that simple, nor is that entirely practical. It's not the companies you need to put pressure on. I would image that some of them aren't entirely excited at the idea of working with the NSA, but they aren't given much choice.
The unfortunate truth is that lobbying DC is the most effective way to enact this kind of change. You can do this online to some extent by using services like Votizen.com. Lobbying by Silicon Valley and others in tech certainly worked for the JOBS act.
As a non-US citizen I can't.
I just spent about 40 minutes crafting a long email that I sent to about 40 family members and close friends detailing why I thought people needed to contact their elected politicians, sign the https://optin.stopwatching.us/ petition, etc.
Seriously, if we can, as individuals, each change several people's minds on this issue, that helps.