A few useful classes to use in Joomla (at least in the Protostar template).

• Menu horizontal rather than vertical
  • nav-pills
• Figures and images
  • pull-left
  • pull-right
  • <div style="clear: both;"> </div> (not a class but useful)
• Images
  • img-rounded
  • img-polaroid
  • img-circle
• Tables
  • table-condensed
  • table-bordered
  • table-striped
  • table-hover
• Lists
  • unstyled
  • list-condensed
  • list-striped
  • list-bordered
• Responsive
  • visible-phone - visible for 767px screens and below
  • visible-tablet - visible for 979px to 768px screens
  • visible-desktop - visible for 980px screens and up
  • hidden-phone - hidden for 767px screens and below
  • hidden-tablet - hidden for 979px to 768px screens
  • hidden-desktop - hidden for 980px screens and up