http://en.wiktionary.org/wiki/pants http://en.wiktionary.org/wiki/ostensibly
http://www.google.com/dictionary?aq=f&langpair=en|en&... http://www.google.com/dictionary?aq=f&langpair=en|en&...
As a plus, Wiktionary lets you download their data :). If Google opens this up, then it could get pretty interesting
Good dictionaries are hard to build. At the same time, the web isn't constrained by space the same way a physical book is, which means that a result should have even more information. You shouldn't accept an online dictionary that gives you only one simple usage of a word.
A good dictionary will list the short & sweet definition, alternative definitions, forms, example usages, pronunciation, history, usages in various situations/jargon, idioms, and word history. This dictionary just points you to a wiki.
Van Dale gives you this: http://dl.dropbox.com/u/381493/van_dale_slim.jpeg
http://www.mijnwoordenboek.nl/
"Slim" isn't a very good example for that dictionary, but check out something with a lot of possible EN-NL translations, usages, and jargon.
http://www.mijnwoordenboek.nl/vertalen.php?src=NL&des=EN...
That site refers you to "Babylon 8", another installable dictionary which just came out with a Mac version. I'm not sure if it returns the same results as the site, but if it does I'd say it's a pretty good competitor for the VDGW (which is truly fantastic, itself).