There are some website that are creating a great list of theme that are completely free and you can useful for you to pick themes for your website.
Colorway is Simple, Elegant, Responsive and beautiful Theme with Easy Customization Options built by InkThemes.com. The Customization Options includes using your own Logos, Backgrounds, Analytics and your own Custom Footer Texts and Analytics that can be tweaked using Theme Options Panel. Colorway Theme is Single Click Install feature, Just press activate button and your website will get ready with all the dummy content.
These theme is completely free and can be downloaded from wordpress.org
Free theme that you can easily download from the link given below Variant is a Landing Page WordPress Theme that’s perfect for creating a landing page website. Variant is completely responsive and gives a nice look to your website.
The BlackWell for WordPress is simple and beautiful with lots of customization options that can tweaked by Theme Options Panel like logos, intro texts and background. BlackWell Theme supports five widgetized areas (two in the sidebar, three in the footer) and featured images (thumbnails for gallery posts and custom header images for posts and pages). It includes stylesheets for print and the admin Visual Editor, special styles for posts in the “Fullwidth” and “Gallery” categories, and has an optional one-column page template that removes the sidebar.
Using ReThink Theme you can easily create the products review website, its really simple and supereasy. Easily promote the products online using this elegant designed review theme. ReThink Theme is built to make your earn money online. Features, easy to use Custom Fields to setup Rating for various products aspects and product Affiliate Links.
I think these themes are really good for your existing or new website. So you can surely pick theme up.