Well I suppose you could consider Courseans of Idra a "guild" of sorts. That and the Scaled. There are plenty of merchant houses but I don't think there's any formalized guilds between them.
Oh well I haven't thought of many since guilds indicate some measure of cilivization. There's some but not enough to support guilds. Regional gangs of thieves might work together, but most I think survive by themselves.
Well I believe there will be a Fighter Guild (of sorts) when the second player's Guide (Fighters and Barbarians) comes out. So perhaps they'll have some answers. (After all not everyone is a BORN fighter. )
I was wondering the same thing for the larger cities in the setting. I have secrets & societies, which is a really cool book and helps a lot for the much larger organizations, but since its not mentioned in the Ghelspad book, would cities like Hollowfaust and Mithril have smaller thieves guilds?
hollowfaust would be a bad place to run a theives guild (not saying it couldnt be done but you would need to stay way below the radar.- final forfiture is a real stiff penalty)