The QRP-TECH yahoo group is a group for the exploration of the radio art through investigating and building low powered radios.
Chuck moderates the QRP-TECH Yahoo Group, His website shows some of the projects that the group has undertaken over the years as well as has a link to his excellent Lab Book - a guide to homebrewing that I wish I'd seen before I got started.
A source for new air variable capacitors in all sizes along with associated accessories (vernier drives, etc)
Largely focused on crystal radios, they also provide new air variable capacitors, though only in double and single ganged 365pf varieties and with vernier drives. Plus everything you would need to make a crystal radio.
20 Meter spots reported by DXSherlock and other spotting networks.
Propagation planner- great for knowing what- if any bands are open in the direction that you are planning on working.