The SharePoint 2010 ribbon, I find, is an unwieldy beast, when not actually in use it still takes up 43px in height of your screen real estate, and trying to fit that into even a relatively low-touch branding project isn’t easy.

Consider the OOTB ribbon shown below.

Or an OOTB ribbon on a recent project (the ribbon bar is shown in black for reference)

It takes up a lot of space, however this can be improved by reducing the space taken up by (the height of) the ribbon group tabs, which when in a resting state, aren’t shown, as you can see above.

In your CSS file or masterpage add the following CSS

.ms-cui-topBar2
{ height:auto;min-height:25px; border-bottom:0px;}
.ms-cui-TabRowLeft
{ margin-top:1px; }
#s4-ribbonrow,
BODY #s4-ribbonrow
{ min-height:25px; }

This removes the explicit height (set to auto) and changes the min-height to 24px (which you can adjust to whatever you need accordingly).

Now add an EditModePanel to your masterpage, add a script block and add the following CSS – this simply reverts the previous CSS settings

.ms-cui-topBar2
  { height:43px; min-height:43px; }
  
  .ms-cui-TabRowLeft
  { margin-top:1px; }
  
  #s4-ribbonrow,
  BODY #s4-ribbonrow
  { min-height:43px; display:block!important; }

This also works for site pages – navigating to a document library, shows the document library ribbon controls when they’re activated