We`ve used;
- Cms Made Simple Core
- Front end user / Custom content for client login
- the form module (much easier then building your own forms)
- .htaccess for pretty urls
- and the lovely Jquery javascript library
- thickbox plugin for jquery for the clickable images.
The "Whats your flavour?" stylesheets switcher is build with Jquery, same goes for the slideshow in de header.
The "Headlines" has an optional button to show another 5 headlines (click on "toon meer headlines" ) when opened click on "sluit extra headlines" to close them, also done with jquery.
Below the "Contact us" heading you can show / hide a form for ordering our brochure clicking on "Klik hier voor de gratis digitale brochure!" Also done with Jquery.
At the bottom if clicked on "disclaimer" it shows a copyright note which auto-disappears after 4 seconds.
The services(diensten) page submenu is done with jquery also, the text can easily be changed in the admin, same as normal, its just uses jquery to hide the parts not selected.
XHTML should be valid, at least last time I checked it was

CSS isnt valid.
We stilll need to add the offline work we`ve to our portfolio so that page isnt finished yet.
you can check it out at: http://www.signex.nl
We have decided this time, not to care about 800*600 (about 3% of our visitors in 2006) so visitors should have 1024*768 or above.