There are many good modern rock bands that play traditional hard rock, but most of them do not get very popular.  Only a select few become really successful, and help keep hard rock mainstream. My favorites among those bands are: The Answer (blues and hard rock), Airbourne (simple hard rock like AC/DC), Wolfmother, and Black Country Communion (both are a slightly more progressive style, akin to Led Zeppelin).
Also, while I'm plugging links, you guys should totally check out the comic Maybe Too Metal! The guy and gal who draw it are awesome and it will make you LOL out loud.
Well, that's it for Rock History Week! I sure had fun with it, and if I entertained any of you in the process I guess that's ok, too. See you next week!