infundibulum

I’ve heard mixed reviews of OSX Tiger, but the little dictionary widget seems to be universally popular. There’s actually a class of applications that do something similar on the web, usually through a proxy:

• POPjisyo – Yahoo!ニュース – トップ (Japanese)

• Rikai (Japanese)
• 

  Cymru’r Byd - Welsh

I’d be interested to know of any others!