Like the ModelBuilder of ArcGIS Desktop to run simultaneous geoprocessing tools, is there any model builder available in QGIS?
Sextante is a geoprocessing library that can be used from several GIS applications. I recommend you to use it from gvSIG as i think that it has the best integration. Sextante also allows (if you configure it properly) use algorithms from SAGA and GRASS.
Here you can see a video that shows how the modeler works.
Update: From March, qgis also has a Sextante plugin that works really well.
GRASS has a model builder that works pretty well (don't know how it compares to the Arc* one).
Victor Olaya, the developer of Sextante is currently working on Sextante for QGIS. It's work-in-progress and not yet ready for production use so use with care. You can watch a short demonstration of the Sextante model builder here: http://www.youtube.com/watch?v=LTUu-I2ouqU
Update Nov 2012: Sextante for QGIS is developing very well, as you can see eg. in this new case study: http://www.qgis.org/en/community/qgis-case-studies/pinhel-portugal.html
Update Jan 2016: Sextante is now a core plugin in QGIS recent versions, and it's called Processing. Check more information about in the QGIS Users Manual - QGIS processing framework. You can also get information about how to use the Graphical Modeler in here.