Sharepoint Ribbon bar is occupying more height space in our application and the business users want this to be avoided somehow. Can anyone suggest any other alternative UI to minimise the Ribbon Control, alternative UI suggestions, or can the height of the ribbon bar be decreased ?
For the most time, only the Browse tab is displayed on a portal page. So you can start from re-arranging or styling the "s4-titlerow" element:
produces the following look:
Obviously the title area is hidden in this case, but you can move it somewhere else and re-style it so it will occupy less space on the page.
I recently wrote a blog article on how to hide the ribbon by default but give users the option to display when needed: http://www.thelineberrys.com/default-category/option-to-show-the-sharepoint-2010-ribbon-when-hidden-by-default-2.html
If you incorporate this into your masterpage, then you could also reduce the height of the s4-titlerow to gain a lot more real estate at the top of the page.
There is always also the option of using the SP 2007 masterpage (uiversion 3) in SP 2010. By doing this you have much more space at the top and don't have to use the ribbon at all. Unfortunately, you don't get full functionality of SP 2010.