The BeppoSAX view of extreme BL Lacs
  With its very wide energy band (0.1-100 keV), BeppoSAX has played a fundamental role in the blazar field, allowing in particular a better study of the highest synchrotron peaked objects. Here we summarize the results of an observational program performed with the aim to find and study more extreme BL Lac sources. We discuss the SEDs of the observed objects and their impact on the "blazar sequence" scenario, and consider their relevance as possible TeV emitting sources. 
L. Costamante, G. Ghisellini, A. Celotti, A. Wolter