Once there were dedicated sw for that and probably will still be, but there is a trend to just use a regular bowser:

http://www.wilmaa.com/

Has nice overview picture and shows how many user watch what channels, so you find interesting things.

http://watch.zattoo.com/

Had a dedicated player, that is now badly supported for Linux. So just the browser version can be used. Many nice features that the player had have been added as well.

Hint: Use a standalone Electronic Program Guide viewer as described in the Epg (Electronic Program Guide) section.