Hoi Marijn,
There are several things going on on your site that break jQuery.
First, there seems to be something very funny going on with the JQuery Drop Down Menu... Apart from the fact that the source code of the main menu seems to have been copied twice into the inline stylesheet in the head section (how did that happen?), it loads it's own version of the jQuery library on top of the one from WordPress itself, that is already included.
Second, there is a third instance of the jQuery library loaded in the footer. I think it is the MailPress plugin doing that.
Loading jQuery two times too many will certainly have its effect on your other plugins that depend on jQuery: Contact Forms 7, WP Table Reloaded, Cimy Header Image Rotator and Easy FancyBox.
Start by disabling the two offending plugins JQuery Drop Down Menu and MailPress and see if it works properly then.
Then contact the respective plugin developers and ask them to switch to the official method of including jQuery: wp_enqueue_script() with 'jquery' as dependency, not directly including the script itself.
Groet,
Allard :)