Quick Offline Lookup

OmniDictionary is a window that pops up, either independently or via the services menu, by which you can look up the definition of a word. It does this by searching various online dictionaries, but by navigating to the Mac OS X DICT page at ropersonline.com you can download a complete package of dictionaries for use offline.

The dictionaries package is pretty huge at 36 megs, but it's oh-so great having a dictionary literally built in to the OS.

Of course, all of this is redundant if you have OSX Tiger with its own built in package...