Here are some great resources for SketchUp plugins. Most of them offer free or pay per script downloads. Just download the .rb or .rbs files and place them in your SketchUp plugins folder. The plugins will automatically load when SketchUp is opened. They will be accessible as a menu item or in the SU context menu or some of them even bring their own toolbar + icons. Some will work only with the Pro version of SketchUp but most of them are okay with the free version. I you go to Window>Preferences>Shortcuts you can assign your own keybord shortcuts to those commands you want to use more often. You will be surprised what an amazing range of possibilities this extended SketchUp platform offer.

Have a look :

http://www.crai.archi.fr/RubyLibraryDepot/Ruby/RUBY_Library_Depot.htm
http://www.scriptspot.com/sketchup-scripts
http://www.smustard.com/
http://www.errorinitus.de/#Software

For more in-depth information on Ruby Scripts go to the SketchUp Wiki.