Pending the transcription of the 1802 first edition of Natural Theology for this site, and important later editions, this link will provide the text of the online text of the 1809 12th London edition.
Additionally, this link offers an extensive archive of classical texts in the Natural Theology genre.
Finally, there is a new edition published by Oxford University Press in 2006, edited by Matthew D. Eddy & David Knight.
For some brief observations on Paley and Natural Theology and the dispute over intelligent design, see here.
It is assumed that users of this site will also be interested in the websites of the Darwin Correspondence Project, and Darwin Online