Ade Weiss' The Joy of QRP.
VK3YE 10 steps to QRP success
QRP Calling Frequencies
There's a considerable overlap between QRP and homebrewing. Sure, many QRPers have commercial QRP equipment and many homebrew projects are not QRP, but still, homebrew and QRP do go together.
QRP Homebuilder archive (40 Mbyte PDF). See also Popcorn QRP.
K7QO's QRP Lab Notebook (large). He also has Norcal's QRPp Journal archived.
The SPRAT Pixie File.
W7EKB's Glowbugs Web Pages.
Ashar Farhan VU3ICQ's BITX also available in kit form.
Michael J. Rainey AA1TJ -- if transistors are too high-power for you and you'd rather use tunnel diodes. Also, Pekka Ketonen OH1TV, OH1O, OH1WX.
AmQRP.org HOMEBREWER No. 5 -- The Handyman's Guide to Understanding Transistor Datasheets & Specifications by Paul Harden, NA5N.