All four varieties of the Canon 70-200mm "L" zoom are renowned for being ultra-sharp, and the latest incarnation of the f/4 IS version doesn't disappoint.  The Image Stabilizer system has been upgraded to offer 4 stops of compensation.  With reasonable technique, you should expect to be able to take photos with shutter speeds as slow as 1/15th instead of 1/200th.

This lens can be used with a Canon Extender (teleconverter).  The 1.4x Extender makes it a 100-280mm f/5.6 zoom which will still autofocus on all EOS cameras.  The 2x Extender makes it a 140-400mm f/8 zoom which will autofocus on 1D-series cameras.