Links - Dictionaries / Encyclopedias / Grammar

Dictionaries 

Dictionary.com - A good dictionary, gives lots of definitions for a word.

Merriam-Webster Online - This page opens to both a dictionary and a thesaurus, not as many definitions as  "dictionary.com."

Grammar

Blue Book of Grammar and Punctuation - Very useful, I like the punctuation pages.

Common Errors in English - Gives a listing of different words - pick the ones you have trouble with (lots of interesting words).