At Penthouse.com you know what you are going to get- ultra-high "magazine" quality girls doing explicit things. When I saw the tour I recognized lots of famous girls but in the members area I realized they have tons of other hot new girls I had never even heard of or seen anywhere else on the net.
They also have a ton of old Penthouse stuff that goes back to the 1970's.
In the members area, they have navigation of 'Penthouse Pets', 'Videos', 'Galleries', 'Live chat', 'Reading', 'World of Penthouse' and 'Store.' They also have a calendar of their updates where it shows thumbnails of all their updates (7 days a week, nice!)
Penthouse Pets has a directory of Pets by year and by name going back to the 1970's.
Videos has about 100 full length movies where you can jump directly to the scene you want to watch. It also has behinds the scenes videos from Penthouse photoshoots and a bunch of hardcore feeds and a video on demand theatre. 'Live chat' has bi-monthly live video chat sessions with select Penthouse Pets and models and 'Reading' has dirty stories from Penthouse Forum.
Members of Penthouse also get access to PenthouseLetters.com, Variations.com and PenthouseForum.com most of which are erotic reading sites.
Overall, I would say if you are a babe/pornstar fan this is a great site to check out as it certainly has a lot of exclusive material and the navigation and design is top notch.