Who rules the world of widgets? It is difficult to measure, but comScore takes a stab at it with a new ranking of widget providers as measured by viewing audience. The Widget Metrix data is from November 2007 and “measures independent objects that can be embedded or downloaded onto another site and can be used as a tool, have automatic content updates, or are interactive.”

In November, 148 million people in the U.S. saw a widget somewhere on the Web (compared to a total Web audience of 182 million, so 81 percent of all Web surfers in the U.S. saw a widget). Of that, MySpace widgets ruled the roost with a 32 percent penetration of the U.S. Internet audience, followed by Slide and Clearspring (at 22 percent each) and RockYou (at 18 percent). if you add Photobucket (16 percent) to MySpace, both are owned by News Corp., that brings the total reach of MySpace-owned widgets up to 46 percent. It seems like Meebo should be in there, with a reach of about 19 million, which would put it right after iGoogle. Who else is missing?

Update: WidgetBox claims 25 million monthly uniques for their widgets, but says they don’t all get counted by comScore because they use Javascript. Another problem with this list is that there might be double-counting. Clearspring, for instance, puts a tracking embed code in RockYou’s widgets. Like I said, these things are difficult to measure.

Update 2: Gigya chimes in, claiming 35 million uniques. And NewsGator says it has 23 million