EconModel

This site, run by William R. Parke of UNC Chapel Hill, lets students and others run simulations of standard micro and macro models. To run the simulations, you must first download a Windows program. Currently, all models have a free 10-day trial period. Below is a list of the available models. As one can see, they cover a fair amount of undergraduate theory.

Supply and Demand

Who Pays a Sales Tax?

Cobweb Model

Perfect Competition

Monopoly

Price Discrimination

Demand for Labor

Two Goods - Two Prices

Labor Supply

Intertemporal Substitution

The Classical Model

Simple Keynesian Model

IS/LM Model

Mundell-Fleming Model

Real Business Cycles

IS/MP Model

Besides the above, the site also has interesting views of data, such as the yield curve from the 1950s to today and an animated Phillips Curve, as well as commentary on current issues.

http://www.econmodel.com/