You could probably create a list of sites that have a paywall anywhere but I'm not sure if that would really provide a huge benefit.
For me, if a site has a paywall and I'm not willing to pay for it then I'll often read the comments to determine if I want to consider paying for it (normally only after I run into the same wall multiple times) or if I want to go looking on the internet for other reporting on the topic.
Hell, I'll help build the feature its that much of a nuisance...