There are a couple out there.
Webacappella 4 (a French app) runs 79 € or about $100 USD
Adobe Muse - this one is subscription based runs about $15 a month or $180 a year (I am transitioning to this one as part of the Adobe Creative Cloud which is all of Adobe's Apps for $600 a year)
Sandvox - more template based about $80
RapidWeaver - about $80 this one give you a bit more control over design than sandvox but, the add-ons can get spendy
RageSW EasyWeb - Still being beta tested final pricing & release date has yet to be announced
That being said iWeb 3.0.4 does still work with Lion & Mountian Lion
My iWeb site: http://jeffnitschke.com
And my Muse experiments:
Hi emanske –
You could also try Freeway. They make Freeway Express which is very cost effective as well as the regular full version of Freeway. It's relatively easy to learn though not as minimal as iWeb. One advantage it does have is you can start with a blank page and don't need to rely on templates which is what made iWeb so good.