Those of us who are studying on our own often find that books with answer keys are invaluable. I have come upon many of these at Google Books and The Internet Archive. These are all free pdf downloads. Try a few out and come back and post a review or two:

• Arnold, T. K., 1849:
  First Greek book
  Answer Key

• Arnold, T. K., 1850:
  Practical Introduction to Greek Prose Composition
  Answer Key

• Arnold, T. K., 1852:
  Second Greek book
  Answer Key

• Dunbar, G., 1829:
  Introductory exercises on the Greek language
  Answer Key

• Jackson, B., 1875:
  First steps to Greek prose composition
  Answer Key

• Jackson, B., 1880:
  Second steps to Greek prose composition (Key Only Right Now)
  Answer Key

• Johnson, W. R., 1829:
  Introduction to the Greek Language (Key Contained)
  Null

• Kuhner and Taylor, 1853:
  Elementary Grammar of the Greek Language: Containing a Series of Greek and English Exercises
  Answer Key

• Kynaston, H., 1879:
  Exercises in the composition of Greek iambic verse
  Answer Key

• Morris, W. H., 1881:
  Greek lessons; showing how useful and how easy it is for every one to learn Greek
  Answer Key

• Sidgwick, A., 1877:
  Introduction to Greek prose composition, with exercises
  Answer Key

• Sidgwick, A., 1880:
  First Greek writer, with exercises
  Answer Key

• Squire, E., 1833:
  Exercises for Greek verse (Key Scanned Together with Text)
  Null

• Wilkins, H. M., 1880:
  New Greek delectus
  Answer Key

(A similar list for Latin books is already available in the Digital Resources Blog).