Not being a big fan of premium themes I still think they have their place and themeforest is probably one of the most popular sites where you can find all sorts of themes for different jobs. After having a quick snoop here are what I think are the best corporate websites.
Display
Suitable for a corporate business that includes a portfolio, some of the features include a 3D slider, 3 colour themes, Valid XHTM Strict1.0 and CSS 2 .1, tableless Design, multiple template files, jQuery functionality and original PSD files for designer editing.
inFocus
A professional looking corporate website with 3 stage jQuery slider, 3 layout portfolio, multiple page layout templates, Valid XHTML, jQuery dropdown menus and PSD files for further editing.
Striking Premium
A significant theme with a multitude of flexibility Valid HTML 5, Cross Browser Compatible including IE 9 and FF 4, 16! Yes 16! Integrated Admin Panels, 4 Different Sliders! Nivo slider! Anything Slider! 3d flash Image Rotator! Accordion slider! Slideshow shortcode, Unlimited Colors, Background loader, 9 Websafe Fonts 45 Cufon Fonts 45 FontFace Fonts.
Unite
A premium Corporate theme with 5 skins that include textured and dark backgrounds, other features include: Valid XHTML Strict/CSS, jQuery cycle and Gallery View, Dropdown Menu, PSD files, QuickSkin™ file for fast and easy design customization, Contact form with dynamic javascript validation, Portfolio with themed preview windows, 2 different themed login options, Cross Browser Compatibility (IE 6, IE 7 , IE 8 , Firefox, Opera, Safari, Chrome)
Karma
Super clean design build on an intelligent framework, a great corporate website for beginner or advanced users. Features include: Administration Panel, 3D Sliders, Shortcodes, 20 Color Variations, Drag-to-Share Bookmarking, Amazing Point and Click Shortcode Manager, multiple Sidebars, Unique Page Templates, 7 Gallery Layouts, Pricing Tables, Powerful Contact Form Builder (with reCaptcha), Complete Instructional Training Videos, XML Demo content for blazing fast setup, Customer Service Support