In general, I've found that most people's favorite topic to talk about is themselves. So when I'm unsure what to talk about next, I invite others to share projects they're excited about or how they started their careers. I try to ask open ended questions that make it clear that I'm interested in stories as opposed to quick factual responses. Often I hear more interesting stories than I would've known to ask about.
By inviting people to talk about themselves, you're more likely to hear from people who are less comfortable self-promoting. Besides, you've already heard from the self-promoters, whether you wanted to or not. Everyone appreciates being given permission to share without being perceived as a bragger or overly self-obsessed. And, people who're more self-conscious often have interesting / novel things to share. They (we) just need a little encouragement.