IBIS (Input/Output Buffer Information Specification) is a behavioral modeling specification for characterizing the inputs and outputs of integrated circuits. This 7 minute video shows how to use them in a signal integrity workflow. The ADS Transient-Convolution Simulator is used to determine the eye diagram and jitter decomposition from a schematic that includes IBIS models from two semiconductor companies (Xilinx and Micron in this example) joined with a channel model consisting of traces and vias.
Anders Ekholm, the Librarian of the IBIS Committee, maintains an IBIS Model Suppliers directory.
Teraspeed Consulting IBIS Resource page also has a comprehensive list of models and all things IBIS.