The Lexicographer's Rules

One of the more interesting aspects of the new Shorter Oxford English Dictionary is that the editorial team, lead by Angus Stevenson, (not Jesse Sheidlower, as mistakenly reported by the American Spectator; Jesse is only doing publicity for the new edition) chose to remove the hyphens from many words. BBC has a fairly decent story about it, and gives these changes:

Became two unhyphenated words
Fig leaf
Hobby horse
Ice cream
Pin money
Pot belly
Test tube

Became one word
Bumblebee
Chickpea
Crybaby
Leapfrog
Logjam

I should also add that if cost is not an object, the Shorter is the dictionary I recommend as a reliable dictionary for household, office, or school use. It does tend to skew a bit British, but with the latest edition, I gather that much more attention has been paid to making sure that North American terms, meanings, and pronunciations are included.

If you're more price-conscious, I now recommend Webster's New World College. This is a change over past recommendations.

If you insist on a free dictionary, then I recommend OneLook, where you'll find several reliable dictionaries indexed and searchable from a single interface (including my Double-Tongued Dictionary).