KnitMap lets you find yarn shops all over the US, Canada and UK. Users can comment and help keep the site updated. You can post pictures, comments, ratings. It specifically lists what type of store it is, whether it has has seating, refreshments, classes or just strictly yarn.
Found this little gem while bored, even though I haven't knit seriously in ages. Longing for it. I commute an hour and a half each way now to work and my fingers are itching except my brain keeps shutting down and fall asleep. Maybe I should bring a little something, especially when winter time comes. It'll keep my hands warm...maybe.