i've read the replies and must say that all the free scripts you can use are worthless if you plan on your site becoming a high traffic site. most of them, like joomla, drupal, phpnuke, will have features you don't need, might have bulky code, may not be able to handle high traffic loads, may utilize all server resources, etc. even wordpress cached at high traffic might be a bit of a drag. i suggest finding a competent coder who is NOT outsourced, who has samples of work running at high levels of traffic with very little bugs and low sql queries, and who can develop a site that creates flat files and caches itself.
This will be better for high traffic website. Many high traffic websites are using self made scripts or similar ones ..
I use Joomla! for almost all of my sites except for blogs. For that I use Wordpress. Once of the nice things about Joomla is you can make it look however you want.
I have a Joomla site which gets in excess of 30,000 unique visitors daily. Joomla is not light but a good server with lot of RAM is more than enough. -Princy
I think one should be assertive when he/she says that this one is good or that one is good plus the source from where to get that script