The one I always use is Heavens Above
But wait, there is even cooler stuff out there! want to see if the ISS is going to pass in front of the sun or moon? There is a page for that! Want to have a quick look at the weather, and see if there is going to be an ISS pass visible? Clear Outside has you covered! Want to find a nice dark spot to see a meteor shower? Dark Site Finder has the most current light pollution maps, but be warned they are still out of date and the sky will be brighter in most spots than the maps say. They also have, under the 'Weather' tab a good guess as to water vapor and cloud cover for the next week.
And then you have the astronomy standard of Clear dark Sky which will only do weather and a guess as to light pollution levels based off the 2001 (not 2012) map.
I'm sure there are more satellite pass predictors out there but Heaven's Above is the one that has the API that the Apps use. And it does Iridium Flares.