Decker - Reading Koine Greek - This is the main textbook we will be following.
Croy - Primer of Biblical Greek - A good textbook in Biblical Greek. The explanations are short and to the point. A lot of exercises.
Hansen & Quinn - Greek An Intensive Course - A standard textbook in Classical Greek. Very in-depth grammar.
David Alan Black - Learn to Read New Testament Greek - Another good textbook oriented toward New Testament Greek.
I can also recommend the textbook and the workbook by William Mounce. However, the electronic versions I have are not good.
StepBible - Very flexible website. Allows to see the Greek text by itself, or with a chosen translation. Text is clickable, with information & parsing for each word. I would recommend using "SBLG" as your Greek Text. It also includes limited Apparatus.
BibleHub & Blue Letter Bible - Similar Interlinear Bibles. Clickable text on the website. Limited functionality.
Kata Biblon - Simple Greek Text. Clickable to reveal translation, information about words, including inflections. Includes limited Apparatus, which is displayed better than StepBible.
GNT Reader - Greek Text with one of the most extensive Apparatus available on the web (click on the verse).
SBL Greek - Greek Text with limited apparatus, ready for download.
Kata Biblon - Similar to NT on the same website. One of the best available versions of Septuagint.
StepBible - Similar to NT on the same website. I would recommend using "LXX" as your Greek Text.
BibleHub - A good resource to start.
Kata Biblon - A good tool to use along with BibleHub.
Mounce's Dictionary - A good and simple dictionary, similar to Kata Biblion.
Blue Letter Bible - A good resource that has many additional features that BibleHub does not.
Wiktionary - A useful tool for basic translation, declensions\conjugation and etymology. Requires you to search in Greek. Hence, you have to either install a Greek keyboard or copy the word from somewhere else.
Perseus - A resource that focuses on Classical Greek.