Rob,

I agree entirely with both Jason and Jeff - ask them.

A lot depends on the kind of folks on your lists but I might tend to be a bit more vaugue on what I ask too. In other words instead of asking what types of products they are interested in - I might ask where could they use the most help. What would you like to see from my emails/newsletters?

Think more in terms of the relationship you are building with your subscribers - this stuff isn't a one-time deal but you can ask them different things again and again.

Hope this helps,

Andy