Once I figured out that you can add "interactive" to any search and then find--surprise!--a bunch of interactives (sometimes these things take me far too long to think up!), my pathfinders became a lot more fun, and teachers are delighted with the results, often using the interactives in class. Here's a list of some of my favorite collections.
NOVA Interactives: Crosscurricular
Annenberg: Some are pretty lame, but some, like the great Amusement Park Physics are classics.
Shodor.org: A great collection of math interactives.
Council on Foreign Relations: Some amazing guides on Global Warming, Iran and more.
The Guardian: My favorite British newspaper offers a collection on everything from the Euro crisis to Jimmy Savile (whoever that is!)
MOMA (They actually have a LOT more than this! Just Google MOMA and interactive. I wish they'd put them all on one page!)
PBS Learning Media