Here are some free eBooks/resources on some of the most popular GRE topics!

A Complete Guide to the GRE: An introduction the GRE format, concepts, strategies, etc.

Attachment:

Magoosh GRE eBook.pdf [1.75 MiB]
Downloaded 1125 times
Vocabulary help:

Complete Guide to GRE Vocabulary: Themed word lists (also with definitions and example sentences).

Attachment:

Magoosh-GRE-Vocab-eBook.pdf [1.72 MiB]
Downloaded 879 times
Math formulas:

GRE Math Formulas: A list of all of the math formulas you should review and memorize for the GRE Quant section.

Attachment:

Enjoy!