Richard has a good wrap-up of the Top Ten Web 2.0 moments of 2005. He has started adding a few of the others like 'Google Maps mashup'. One of the big ones for me is the emergence of the Web 2.0 'framing' - it defines a whole new generation of 'software as a service' and ushers in a new level of utility in terms of how we use software.
Another Top Ten Web 2.0 moment - and it was more of a steady drum-beat than a moment - was the emergence of the Wiki as a participatory platform. And the emergence of new challenges to public Wiki platforms - like inaccuracy in entries.
I'll also look back on this year as the year that the Participatory Era took hold. Suddenly millions of users really started participating in the conversation, establishing new dialogues and framing new debates. Recommenders started taking hold of products' destinies. And new participatory engines - from Blogs to Wikis and Ajax-based applications like Meebo - emerged.