Is there any web site that you can recommend in which I can find premium (beautiful looking and professional) web site designs(themes) specific for mobile web sites? (paid or free)
If you're using WordPress, wptouch is awesome. See: https://www.bravenewcode.com/store/plugins/wptouch-pro/
Other than that, there are a lot of really good development frameworks emerging for mobile applications; two good ones are cssgrid (Fluid-width http://cssgrid.net/) and Less Framework (http://lessframework.com/).