See the link at the bottom of this page for SPICE models for MOSFETs from STMicroelectronics (formerly SGS Thomson):
http://www.st.com/stonline/products/families/transistors/power_mosfets/spice_models/spice_models.htm
A very good book about SPICE component modelling is "Semiconductor Device Modelling with SPICE", edited by Antognetti and Massobrio. Check out your local technical library to see if they have a copy you can borrow.
In that book's chapter 4, three levels of MOSFET model are discussed. I think that most SPICE programs would use the full model, but I don't know that for sure. The simpler models will run faster, but may lose some accuracy in some operating areas. For jellybean power applications of MOSFETs (where you aren't pushing the high-frequency modelling very much), it probably doesn't matter if a simpler model is used. Table 4-1 in the book lists all 36 of the model parameters, with default and typical values, and says what level models the parameters apply to.