So far I have managed to wrangle up a few promising websites. PhET is one of my favorites that I have been using for a couple years and http://astro.unl.edu/animationsLinks.html has some great simulations specific to astronomy. Thanks to Lauri's comment on my last post I have now been able to begin browsing a couple different online lab databases: http://www.jdenuno.com/TechConnect/OnLineLabs.htm and http://onlinelabs.in/subjects. I have also begun searching for simulations relating to the units I am currently working on, and found this collection of resources relating to Properties of Matter: http://www.learningscience.org/psc2apropchangmatter.htm.
My next step will be to choose a simulation for my next unit to begin designing a lab around. I also need to identify a good place to share the labs I create, specifically for those that do not use PhET simulations (PhET allows you to upload lesson plans to their website). In the meantime, I would be interested to know if you have any other simulation resources you like or if you recommend a website for sharing lesson plans for online labs.