The REDOX simulation that Tom has is perhaps my favorite virtual lab of ALL time. I have a write-up on my web site for free! http://www.adriandingleschemistrypages.com/wp-content/uploads/2013/10/aplab03b.pdf

I used "Electrochemical Cells" by Gary L. Bertrand at the University of Missouri-Rolla: http://web.mst.edu/~gbert/Electro/Electrochem.html. Students can change electrodes and solutions and measure the cell voltage. They can then use the standard cell voltage and the Nernst equation to calculate theoretical cell potential of a non-standard cell. The simulation also allows them to change the concentration of the solutions in the cell.

Thanks, Kaleb!  I will give these a try.

Tom Greenbowe out of Iowa State has an excellent bank of simulations. Here is a link to one that I think may be what you need: http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/electroChem/voltaicCellEMF.html Here is a link to the prelab for that sim: http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/NernstCellPreLab.html Here is a link to the index of all sims: http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/animationsindex.htm Here is a link to raw files that I like to peruse: http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/