If you want the best CMS out there in terms of features its Joomla. With 1.0.13 you can do whatever you want - blog / forum / video / images / community / etc etc. To get a full idea of what extensions are available for Joomla see
http://extensions.joomla.org
There are also a lot of template clubs and commercial components available for this. My dedicated Joomla site -
http://www.jooms.com - we do complete solutions from $299.
Here are some sites done by us -
http://www.mumbaimart.com
http://www.maal.biz
http://www.glamzone.com
http://www.golfkraft.com
http://www.revayur.com
http://www.unijules.com
http://www.mediawiz.biz (Web Developers since 1998 - My co.)
http://www.mediawiz.co.in
http://www.chaloindia.com
Its extremely extensible due to the 3PD community. 1.5 the code base is phenomenal but I think you're going to need to code all the solutions yourself (some like forum / events calendar etc will be available).
Drupal comes a close second and is actually better than Joomla for native SEO. It lacks in extensions for increasing functionality of the core code or even themes. So if you're doing content only sites its a much better option.
Wordpress is third, easy enough but a pain to update everytime theres a new release or even to tackle compatibility issues between plugins. But its LOT more powerful that it looks. It can be easily used only as a static site with decent seo out of the box. It also has tons of plugins to allow you to make full use of the social web or web 2.0. Also, creating custom skins for this is the easiest.
We've made some demo sites with this,
http://www.blog-sale.com
http://www.hitpr.com
plus I also blog on this -
http://www.mwzd.com
The fun bit is you can actually use Joomla AND Wordpress together via the JD component/bridge. You can also use Joomla + SMF or Joomla + Gallery or Joomla + Coppermine or even Joomla + Gallery + SMF.
Yes it has a learning curve, yes its not easy to get your head around but if explained properly its simply the best CMS out there. And demos / tutorials dont really help. You need to understand the concepts and then implement the site as per functionality. Most sites with less than 100 pages can be done under 24 hours.
Sites that need advanced SEO or Community features can take a week and cost anywhere between $1.8k - $9k.
We've been using Mambo for two and a half years before Joomla and I'm one of the first 900 members on Joomla.org forums. So for us it comes naturally. Drupal is a lot tougher to implement and is recommended only for enterprise projects. Plus low grade architecture can crash for a high usage site, where Joomla.org has about 20,000 visitors per day and runs on Joomla and no problems.
We also have a down and dirty website builder that costs as low as $1.99 for 15 pages upto $4.99 for 500 pages (w/o hosting and per mo.)
Heres the feature comparison for that -
http://web.mediawiz.biz/sitebuilder.php?type=sblite
And heres the demo -
http://web.mediawiz.biz/content.php?action=demo&type=sblite
You can add flash/images/et al. without any problems...try the demo.
For 10,000 sites I think a multi-cms is your only solution though you'll need to custom code it or get it done. Joomla has a multi site installation component, commercial, though its a pain to implement. Nucleus is too flat but easy to implement on multiple sites.
Hope the links will be forgiven, they are just for example purposes. Oh and btw DCG, we are always open for new work.