I agree, Piggot's books are authoritative and reliable, although some of them are a little long in the tooth (best to get the latest editions).
Besides the titles already mentioned, in 1991 Piggot wrote another book called "Gliding Safety" that is worth checking out. It has a chapter in the back on power pilots converting to soaring, which provides several tips that might be helpful.
Thomas L. Knauff is an American soaring authority that is well respected this side of the pond, and he has written a book called
"Transition to Gliders: A Flight Training Handboook For Power Pilots", which I think was originally published in 1984 (2nd edition came out in 1990). You can locate copies on Amazon, or buy direct from the author at
http://www.eglider.org/
Finally, the SSA has an interactive CD-ROM for power pilots converting to sailplanes [
http://www.ssa.clientreadyweb.com/in...&prodid=478676], but I doubt that you need that unless you really enjoy using computers.
MLS-12D
P.S. You can find a pretty comprehensive list of soaring books at
http://w3.gwis.com/~mks/book.htm, but don't worry about running around buying up a huge personal library at this time, you'll be quite all right with one or two books giving you the basics.