The GFS (Global Forecast Model) is a model from the National Weather Service. The model forecasts up to 16 days out. It is updated 4 times a day, and is considered one of the 'big guns' in the weather model world. For a simple forecast, use the GFS Model Unisys link.
The RUC (Rapid Update Cycle) model is a short range model updated every hour. It goes out to 4 hours. The RUC is going to be replaced in August 2011 by the Rapid Refresh model. For a simple forecast, use the RUC Model Unisys link.