What are some of your favorite cafes in Manhattan with free wifi and decent coffee or tea?

The really important thing is a steady wifi connection in this case. I know at many coffee shops, you can piggyback off of unsecured networks. But... where do you go when you want to linger and type up something?

And when you go, do you feel compelled to tip extra because you're using the free WiFi? Or buy an extra scone or something?