The CellML language is an open standard based on the XML markup language. CellML is being developed by the Auckland Bioengineering Institute at the University of Auckland and affiliated research groups. http://www.cellml.org

The purpose of CellML is to store and exchange computer-based mathematical models. CellML allows scientists to share models even if they are using different model-building software. It also enables them to reuse components from one model in another, thus accelerating model building.

SBML defines machine-readable representation of biological network models that are specifically aimed at simulation and sysem analysis.
http://sbml.org/

SBGN defines human-readable representation of biological network models in the most expressive and consistent manner.
http://sbgn.org/

The first SBGN Process Diagrams Level 1 specification is released (23 Aug.'08)
Download the specification and tell the community what you think!

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BioPAX (Biological Pathways Exchange) is a collaborative effort to create a data exchange format for biological pathway data.
http://www.biopax.org/