Flickr.com is an insanely great service. It's a very-well thought out and constantly improving photo sharing web site. There appears to be virtually no absolute limit to the number of pictures you may place. It is a monthly quota. They're encouraging people to use their site as a constantly updating "Photo Stream", while making it very easy to manage pictures in batches.
Based on textual information associated with pictures, the site serves mostly relevant ads from Google's AdSense program, which appears to be a part of how they're planning to subsidize their service. Members can easily associate an unlimited amount of arbitrary "textual tags" to each picture, which instantly builds various "views" of one's album: