The Greek New Testament Gateway:
Grammars

Herbert Weir Smyth's Greek Grammar (New URL)
      [Chicago Mirror]   [Berlin Mirror]
A complete, on-line grammar available at the Perseus Site.

Herbert Weir Smyth's Greek Grammar (New)
The same grammar, available from Textkit as a PDF.

Overview of Greek Syntax
      [Chicago Mirror]   [Berlin Mirror]
By Jeffrey A. Rydberg-Cox. An excellent resource also at the Perseus site containing "a short description of the elements of Greek Syntax that most students will encounter in first and second year Greek". Each section contains an example that is linked to the texts in the Perseus digital library and a link to Smyth's Greek Grammar (previous link).

Greek Grammar by William W. Goodwin (New)
At Textkit, who write "Goodwin’s Greek Grammar stands with Hadley’s Greek Grammar as one of the most widely used and longest running Greek Grammars in America. The grammar has gone through many editions and reprints for over 130 years, with the last major edition appearing in 1930."  In PDF format.