There are so many great online resources.
Check the STEM Workshops pages and the wiki for lots of ideas and activities. These include informational and interactive websites, experiments, and other hands-on and virtual activities.
Earthquakes & Plate Tectonics
Hurricanes & Weather (and building simple instruments)
Scientific Method & Motion
Solar System & Astrobiology
Volcanoes & E-Missions
Water, Watersheds, Wetlands, Properties, Conservation, Cycles
Energy - Power for a Modern World
Nuclear Energy - Is it a good thing?
This unit plan explores nuclear energy in a constructivist method by asking students to recommend or deny approval for continued operations of a nuclear power plant. A great topic for interdisciplinary planning, it combines elements of chemistry, engineering, math and socio-economic ramifications and opportunities for writing and reading about radioactivity and the scientists behind the discoveries.
Science & Nature
Beautiful and complex, from the minute to the infinite, we humans are just one part of the big jigsaw puzzle. It's easy to forget when in the midst of an urban environment with paved playgrounds - thank goodness for parks and community gardens. Field trips are a must, and museums are a great resource for both virtual and real world forays.
Technology in the form of probes helps students collect data for charting and analyzing, and these have portability options as well.