In the first few dates, I will offer to pay for something small if we have a multi-location date. However, if he turns it down, I just put my money or credit card away. Some guys like to feel that they are treating you so I don't insist on it if they say no.
Other than that, I like to wait until we are exclusive. Then I will make more serious offers to pay. I recently became exclusive with the guy I'm seeing and actually switched his credit card with mine so I could pay for our meal because he didn't want me to pay. :)