I am looking for a legal, online version of the Abhidhamma in English. Can anyone point me towards some good online sources, especially for the major books of the Abhidhamma?
The "Comprehensive Manual of Abhidhamma" is an excellent translation of the Abhidhammattha Sangaha with extensive explanation / charts by Bhikkhu Bodhi. It can be legally downloaded from:
There are scanned copies of some of the Abhidhamma Pitaka available at:
The Pali versions appear to be legal, the legality of the English versions is questionable.
My strong advice to you is to start with the CMA. Only once you have truly mastered this text should you even consider looking at the original Abhidhamma Pitaka texts.
From Preface of this book,
This book is not a synopsis of the Abhidhamma which, in itself, comprises seven volumes of the Pali Canon. Here, some aspects of the Abhidhamma have been related to practice. If this little book helps the reader to appreciate that the teachings of the Enlightened One are never mere theories but always stand to reason and can be verified in the crucible of his or her experience, then its purpose will have been served....