Think that all of the great Web sites have already been invented? Think again. The Internet is evolving in new and inventive ways thanks to mashups that pull data from all over the Web and to AJAX-based interfaces that give sites the same degree of interactivity and responsiveness that desktop apps possess.

To keep you ahead of the curve, we've rounded up 25 innovative Web sites and services that are well worth watching. Some of them help you design your own personalized Web site mashups; others enable you to create video mixes, build wikis, share personal obsessions, and more. But take note: A number of these sites are works in progress, and user-generated sites depend on developing a critical mass of content, which doesn't happen right away. With that in mind, check out the following dot-com destinations. One of them may become the next big Web hit.