A beach?
The street, in a sufficiently large city with a public transport system. Long before I knew anything about PUA I got started on the London Underground. Some of that game is still applicable to a smaller city, because drunken girls do walk from bar to bar. I guess that's "between bars" game rather than day game proper though.
Coffee house can work, but I wouldn't call it high turnover per hour, and you can run into underage problems.
A park loop around a lake where people walk, bike, and rollerblade, in a sufficiently dense metro area. For instance, Seattle's Green Lake. The loop keeps a large numbers of people moving through a small location, and you've usually got more than 1 shot at somebody if you wait a half hour.
I have no idea about sporting events as I'm not into them. But I notice there are a lot of people there.
A stadium concert would be a dead obvious one, but again I'm not into them, and it would get expensive for something I don't care about.
Public festivals periodically turn out huge numbers of people. Seattle had a lot of those. I called 'em collectively "FlakeFests" because they all feel the same to me after awhile. Granola nutters on stage, drum circle off in the distance....
Vast numbers of people go to WalMart, but I don't know if I'd want to game it. I've spent a lot of time collecting signatures for ballot initiatives at WalMart though. I had a legal right to accost people.
