Since people on this forum are busy so I would like to give some suggestions :
could someone recommend some actual textbooks (not study guides) to study from that cover the kind of questions that the GRE asks? (particularly abstract algebra)
1. Cracking the GRE maths
2. Barrison's book which includes 6 practice test
3. REA GRE math practice tests
http://www.amazon.com/GRE-Mathematics-REA-Best-Preps/dp/0878916377- If you can solve all the problems in this book you will definitely get good result
4. Some sample tests posted on this forum - you can find them out
For algebra section I strongly recommend the following book
http://www.amazon.com/Abstract-Algebra-2nd-David-Dummit/dp/0471368571
what are the best approaches to studying and preparing for this exam
it depends on yourself, if your maths background is good you should head to >90%
This forum is the greatest forum for GRE maths, discussing if you have questions