Previous to taking this course I wasn't really concerned about finding new ideas for urban technologies so I really just discovered them casually or accidentally on Twitter. I never sought them out. But since this course began and showed how much cool stuff there is out there I've been looking more. I still rely on Twitter and have gotten some suggestions for follows from the mindmixer. But I have also recently begun watching more TEDtalks.
Another way I have found some cool ideas is, ironically, by abandoning technology all together and just asking people what kinds of things they have heard of. This has been my favorite method.