A mad dash these days for widgets. The most interesting ones of course that ones that can make you money:
Google AdSense - IMHO the original, most widely distributed, and most important "widget" on the internet, by definition of "widget". Though interestingly, almost never referred to as widget.
Tumri AdPod - Rev-share pay per click module focusing on shopping ads from consumer merchants.
Nooked - Seems to be similar to Tumri, though still in private Beta so no preview.
FavoriteThingz - Amazon and Ebay Affliate marketing webstore in a widget.