An old presentation James Strachan gave at CodehausOne August 2003 is available as a PPT
Andrew Glover wrote an interesting article in the "ant.lang.jre" series introducing Groovy on DeveloperWorks
Marc Hedlund has written several very good introductory articles about getting stuff done with Groovy (especially with the SwingBuilder). The index of all his articles can be found at O'Reilly's website.