I've been on the Storium beta for about a week now, and I've joined three different games so far: one is a sequel to Redshirts, one is a Mass Effect game taking place around the time of Mass Effect 2, and the other is a Pacific Rim AU. I haven't yet started narrating my own game, but I do want to give it a shot at some point. So I've been trying to think of what game I might run if I do. Here's what I've come up with so far:
Doctor Who: The S.O.S. Files - This would be the third time I've attempted to run this setting, and the second attempt at doing so in a PbP environment. The concept is that the players are all members of a LINDA-like group based in a small British city which happens to be a hotspot of supernatural activity, set in the Whoniverse.
Planetfall - Having crashed on an unexplored world, the survivors of a transport ship must work together to survive and unlock the secrets of the strange world they have found themselves stranded on. Think Lost...in spaaaaace! This would have been one of my picks for the Primetime Adventures list I did earlier this week, but I didn't think it was all that great an idea. Still, 'Mysterious Island' is one of the starter Worlds available on Storium, and I could probably customise that to make a more sci-fi version of the setting.
Welcome to Night Vale - I'd be surprised if someone hasn't already tried this on Storium, to be honest. If I did go with this idea I'd probably make it about the interns at Night Vale Community Radio. They've got a reason to investigate the strange goings-on in the town of Night Vale, and they're not part of any organisation likely to have a hands-on involvement in those goings-on since the radio station seems to be primarily an observer of happenings in the town, rather than an active participant.
Well, it'd either be the interns or Carlos' team of scientists.
Beyond those three, I'd probably do a generic cyberpunk game or a generic urban fantasy. I might have more ideas by the time I'm ready to narrate something, but at the moment the creative well's running a bit dry. I'll let you know when I do start a game of my own though.