Listmania!
Invaluable Classical Greek books - how to get from 0 to 60.
Learn Ancient GreekLearn Ancient Greek by Peter Jones
Buy new: £7.77 / Used from: £3.50
Friendly, fun, yet rapidly gets you on your journey.
Greek to GCSE: Part 1Greek to GCSE: Part 1 by John Taylor
Buy new: £8.79 / Used from: £5.23
More formal than Jones. An effective appetiser for beginners.
Greek to GCSE: Part 2Greek to GCSE: Part 2 by John Taylor
Buy used from: £4.95
After this, you should be able to have a go at the originals texts... with a decent lexicon.
All the Greek Verbs (Greek Language)All the Greek Verbs (Greek Language) by N. Marinone
Buy new: £10.39 / Used from: £15.59
An absolute Zeus-send for those naughty inflected verbs.
The Pocket Oxford Classical Greek DictionaryThe Pocket Oxford Classical Greek Dictionary
Buy new: £7.27 / Used from: £5.50
An accessible dictionary for beginners. Intermediate and above will need to look elsewhere.
Oxford Grammar of Classical GreekOxford Grammar of Classical Greek by Morwood
Buy new: £9.68 / Used from: £10.57
A handy little reference book or aide-memoire for the main parts of grammar.
Abridged Greek LexiconAbridged Greek Lexicon by H. G. Liddell
Buy new: £25.10 / Used from: £21.80
The abridged version is useful enough for intermediate and above. The full version is a beast!
Marcus Aurelius (Loeb Classical Library)Marcus Aurelius (Loeb Classical Library) by Marcus Aurelius
Buy new: £12.48 / Used from: £15.94
Although much later than Plato et al, I found this a good starting point.
Laches, Protagoras, Meno, Euthydemus (Loeb Classical Library; Plato vol. 2)Laches, Protagoras, Meno, Euthydemus (Loeb Classical Library; Plato vol. 2) by Plato
Buy new: £15.15 / Used from: £9.00
At last - Plato in the original. A most satisfying goal.
Greek GrammarGreek Grammar by HW Smyth
Buy new: £30.09 / Used from: £24.99
A formal and exhaustive survey of Attic grammar.